GIFT  OF 
Dean  Frank  H.  Probert 


Mining  Dept 


•       ,-..•• 


THE 


GENESIS  OF  ORE-DEPOSITS. 


A    TREATISE 


BY  PROFESSOR  FRANZ  POSEPNY, 

OF    VIENNA. 


TOGETHER   WITH    THE    DISCUSSION   THEREOF,   REPRINTED    FROM 

VOLUMES   XXIII.  AND   XXIV.  OF  THE   TRANSACTIONS  OF 

THE  AMERICAN  INSTITUTE  OF  MINING  ENGINEERS. 


NEW  YORK  CITY  : 

PUBLISHED  BY  THE  INSTITUTE  AT  THE  OFFICE  OF  THE  SECRETARY. 

1895. 


?7 


CM 

KiflDH 
KPJ. 


DEAN  FRANK  H  .MO BERT 


MINING  D6PI, 


TO 

MADAME  CLOTILDE 

WIFE,    COMRADE    AND    COLLEAGUE 
OF    THE    DISTINGUISHED    AND    LAMENTED 

AUTHOR    OP    THIS    TREATISE, 

THE    PRESENT    VOLUME    IS    INSCRIBED 

IN    WITNESS    OF    GRATITUDE    FOR    HER    CO-OPERATION, 

AND    SYMPATHY    WITH    HER    BEREAVEMENT. 


M127134 


PREFACE. 


THE  name  of  Franz  Posepny  appears  in  the  first  volume  of  the 
Transactions  of  the  Institute  as  one  of  its  foreign  members.  At  the 
Boston  Meeting  of  February,  1888,  he  was  elected  an  honorary 
member,  in  recognition  of  his  numerous  and  valuable  contributions 
to  the  literature  of  economic  geology,  and  particularly  to  the  sci- 
ence of  ore-deposits,  which  has  borne  in  Germany,  at  least,  since 
the  days  of  the  brilliant  Cotta,  the  name  of  Erzlagerstdttenlehre.  The 
views  of  Cotta  and  his  associates,  sometimes  called  for  convenience 
"the  Freiberg  school,",  dominated  for  a  generation  the  current 
theories  and  classifications  of  mining  engineers.  This  is  particu- 
larly true  of  the  United  States,  where  the  excellent  translation  of 
Cotta' s  text-book  by  Prof.  Fjederick  Prime,  one  of  his  pupils,  and 
one  of  the  original  members  of  the  Institute,  was  for  many  years 
the  controlling,  and  indeed  the  only  easily  available  authority  on 
this  subject  in  the  English  language. 

As  a  personal  friend,  diligent  student  and  hearty  admirer  of 
Bernhard  Cotta,  and  no  less  as  professional  critic  of  his  views,  I 
feel  myself  bound  to  say  that  his  theories,  as  stated  more  than 
thirty  years  ago,  are  still,  to  a  surprising  degree,  valid  and  compre- 
hensive. There  is  scarcely  a  single  modern  modification  of  them, 
for  which  he  did  not,  with  intuitive  prescience,  leave  a  place.  On 
the  other  hand,  it  is  a  fair  criticism  of  the  whole  "  Freiberg  school," 
that  it  gave  too  much  prominence  and  attributed  too  much  typical 
importance  to  fissure-veins  of  the  class  represented  in  the  Erzgebirge. 
Such  writers  as  Groddeck  and  Grimm  have  undoubtedly  aided  to 
modify  this  disproportionate  emphasis.  But  it  has  not  ceased  to 
influence  the  conceptions  entertained  by  miners  and  even  by  legis- 
lators, as  the  United  States  mining  law  (evidently  based  on  the 
"  true  fissure-vein  "  as  a  general  type)  abundantly  demonstrates. 

Posepny  had  contributed  to  the  subject  numerous  monographs, 
throwing  much-needed  light  upon  it  from  the  detailed  study  of 
special  mining  districts.  He  had  been  for  many  years  devoted  to 
this  particular  branch  of  geology,  and  had  occupied  for  ten  years  a 
chair  as  professor  in  the  Przibram  Mining  Academy,  dealing  ex- 
clusively with  the  theory  of  ore- deposits.  When  I  urged  him  to 
contribute,  for  the  International  Meeting  of  the  Institute  in  1893,  a 
paper  on  that  subject,  I  did  not  venture  to  expect  so  generous  a 
response  as  I  received,  in  the  free  dedication  to  the  Institute  of  a 
treatise  comprising  a  summary  of  the  views  and  observations  of  the 


VI  PREFACE. 

distinguished  author,  and  covering  the  whole  field  of  his  specialty. 
Besides  its  wealth  of  details,  this  treatise  presents  a  most  interesting 
and  suggestive  attempt  at  a  genetic  classification — a  feature  con- 
fessedly absent  from  most  earlier  systems. 

The  translation  of  Prof.  Posepny 's  work  was  to  me  a  labor  both 
instructive  and  delightful ;  and  I  take  pleasure  in  acknowledging 
here  that  my  task  was  greatly  lightened  in  that  regard  by  the  mar- 
vellous accuracy  and  beauty  of  the  German  manuscript,  the  whole 
of  which  came  to  me  in  the  exquisite  handwriting  of  Madame 
Posepny.  Her  husband  was  for  some  months  unable  to  write,  by 
reason  of  an  injury  to  his  hand.  Probably  he  regarded  this  acci- 
dent as  a  misfortune ;  but  I  trust  he  will  not  be  offended  if  I  say 
that  his  American  translator  had  reason  to  take,  with  gratitude,  a 
different  view  of  it. 

My  translation  of  the  paper  itself  has  received  the  author's  ap- 
proval; but  the  translation  of  his  later  communication,  which 
appears  in  this  volume  in  the  course  of  the  discussion,  goes  to  press 
without  final  revision  on  his  part.  I  can  only  infer,  from  his  omis- 
sion to  return  with  corrections  the  copy  sent  him  several  months 
ago,  that  he  has  not  found  serious  errors  in  it. 

The  presentation  of  this  paper  at  the  Chicago  Meeting  of  1893 
was  the  signal  for  a  lively  and  interesting  discussion  on  the  part  of 
American  geologists.  That  discussion  has  by  no  means  come  to  an 
end ;  and  it  is  likely  that  the  impulse  thus  given  to  a  renewed  study 
of  this  important  subject  will  continue  to  operate  for  a  long  time  to 
come.  It  was,  however,  necessary  to  stop  somewhere,  in  preparing 
the  present  volume  for  the  convenient  use  of  readers ;  and  the  line 
has  been  drawn  at  the  end  of  Vol.  XXIV.  of  the  Transactions  of  the 
Institute,  so  as  to  include,  with  a  complete  analytical  index,  for 
ready  reference,  both  the  original  paper  and  all  the  discussions  of 
it  contained  in  Vols.  XXIII.  and  XXIV. 

R.  W.  RAYMOND. 

POSTSCRIPT. — Since  the  above  paragraphs  were  put  in  type,  the 
tidings  of  the  death  of  Prof.  Posepny  on  March  27,  1895,  after  long 
and  severe  suffering,  have  furnished  a  sorrowful  explanation  of  my 
failure  to  receive  any  recent  communication  from  him.  A  biograph- 
ical notice  of  him  will  be  published  among  the  papers  of  the  Florida 
Meeting  of  the  Institute  (the  first  session  of  which  was  held  on  the 
day  of  his  death)  and  in  volume  xxv.  of  the  Transactions.  In  the 
absence  of  time  and  space  for  other  tribute  here,  I  have  inscribed 
this  book  to  his  wife,  and  prefixed  to  it  a  portrait  of  himself,  for 
which  I  am  indebted  to  the  publishers  of  the  New  York  Engineering 
and  Mining  Journal. — R.  W.  R. 


THE  GENESIS  OF  ORE-DEPOSITS. 


CONTENTS. 

INTRODUCTION. 
PART  I. — GENERAL  FACTS  AND  THEORIES. 

PAGE 

1 .  Systems  of  Classification  Employed  Hitherto,  ...       3 

2.  Standpoint  and  View  of  the  Present  Paper,  ...       9 

3.  The  Xenogenites  in  General,    .         .         .  .         .         .     11 

4.  The  Subterranean  Water- Circulation,      .  .         .         .16 

A.  The  Vadose  Underground  Circulation,        .         .         .17 

Filling  of  Open  Spaces  Formed  by  Vadose  Circulation,      .  .21 

B.  The  Deep  Underground  Circulation,  .         .         .         .24 

Ascending  Waters  Encountered  in  Mines,      .  *  .  .26 

Related  Phenomena  near  the  Surface,  .....        29 

Mineral  Springs  at  the  Surface, ......       34 

Chemical  Constitution  of  Mineral  Waters,      .  .  .  .36 

Minute  Metallic  Admixtures  in  Mineral  Waters,      .  .  .42 

Alterations  Produced  by  Mineral  Springs,      .  .  .  .44 

Structural  Features  of  the  Deposits  of  Mineral  Springs,     .  .       48 

5.  Origin  of  Ore-Deposits  in  the  Deep  Region,     .         .         .51 

Manner  of  Filling  of  Open  Spaces  in  General,         .  .  .58 

PART  II. — EXAMPLES  OF  CLASSES  OF  DEPOSITS,         66 

1.   Ore-Deposits  in  Spaces  of  Discission,       .         .         .         .68 
General  Features  and  Illustrations. 

a.  Ore-Veins  in  Stratified  Rocks,         '.,        .         .         .73 

Clausthal,  73  ;  Andreasberg,  74. 

6.  Ore-veins  in  the  Neighborhood  of  Eruptive  Masses,      75 

The  Erzgebirge,  75  ;  Przibram,  76. 

c.  Ore- Veins  Wholly  Within  Large  Eruptive  Formations,  78 

Hungary,  78 ;  Dacian  Gold-field,  79 ;  Verespatak,  80 ;  Vulkoj,  80  ; 
Comstock  lode,  82. 

1 


2  THE   GEIs7ESIS   OF   ORE-DEPOSITS. 


PAGE 

2.  Ore-Deposits  in  Soluble  Rocks, 87 

Fillings  of  Spaces  of  Dissolution  and  Metasomatic  Deposits. 

Kodna,  SI ;  Offenbanya,  89 ;  Re*zbanya,  90 ;  Eaibl,  93  ;  North  of  England, 
96;  Leadville,  Colo.,  97;  Red  Mountain,  Colo.,  100;  Utah,  101 ;  Ne- 
vada, 101  ;  Deposits  in  Structural  Plateaux,  105:  Valle*  and  Mine  la 
Motte,  Mo.,  106,  107  ;  Wisconsin,  107. 

3.  Metamorphous  Deposits, 108 

General  Features. 

a.  Ores  in  Distinctly  Stratified  Rocks,         .         .         .110 

Deposition  of  Ores  from  Sea-Water,  110;  from  Fresh  Water,  112;  the 
Copper-Schists  of  Mannsfeld,  113;  of  Bohemia,  113:  of  Thiiringia, 

113;  of  Westphalia,  114;  the  Copper-Sandstone  of  Bohemia,  116; 

of  St.  Avoid,  116;  Lead-Deposits  of  Mechernich,  117;  Freihung, 

118  ;  Silver  Reef,  Utah,  119;  Copper-Deposits  of  New  Mexico  and 

Arizona,  120;  Boleo,  Lower  Cal.,  121. 

b.  Metasomatic  Deposits  in  Soluble  Rocks,.         .         .     122 

Calamine-Deposits,  122;  Laurium,  123;  Bohneisenerz  of  Alsace,  125  ; 
Cumberland,  125;  Wochein,  Carniola,  125. 

c.  Deposits  in  Crystalline  Schists  and  Eruptive  Rocks,     125 

Taberg,  Sweden,  126;  Cornwall,  127  ;  Scandinavia,  128;  Ammeberg, 
129 ;  Prettau  in  Tyrol,  131 ;  Lake  Superior,  132 ;  Sudbury,  Can.,  133. 

4.  Hysteromorphous  Deposits, 135 

a.  Chemical  effects,       .         .         .         .         .         .         .135 

Limonite  near  Rio  Tinto,  Spain,         .....        136 

<b.  Mechanical  effects, 139 

Verchoviky,  Surface-Deposits  in  situ,  139.  Theory  of  the  Sinking  of 
Heavier  Constituents,  140  ;  Stream-detritus,  141  ;  Marine  detritus, 
143  :  Kackar  District,  Ural  Mountains,  143  ;  Platinum-placers,  144  : 
Tin-placers,  145. 

'C.  Hysteromorphs  of  Older  Geological  Formations, .         .     146 
Dead  wood,  S.  Dakota,  147;  Australia,  148;  South  Africa,  148:  Bohe- 
mia, 149. 

INTRODUCTION. 

ALL  serious  investigators  of  this  problem  have  recognized  its  com- 
plex character,  and  the  difficulty  of  solving  it  definitively  in  the 
present  state  of  our  knowledge.  Single  and  simple  occurrences  are 
at  present  clearly  understood  ;  but  the  more  complicated  phenomena 
give  rise  to  discordant  and  often  totally  contradictory  views,  show- 
ing that  we  are  still  far  from  the  truth  upon  this  subject.  The  study 
of  it  has  been  the  labor  of  my  life;  yet  I  must  confess  that  the  little 
I  have  here  and  there  accomplished  bears  no  proportion  to  the  great 
range  of  the  inquiry.  I  collect,  nevertheless,  in  this  paper,  some  of 
the  personal  views  to  which  I  have  been  led,  chiefly  in  order  that 
they  may  be  submitted  for  consideration  and  discussion  to  my  Amer- 
ican colleagues. 


THE   GENESIS   OF   ORE-DEPOSITS.  3 

Looking  upon  a  single,  somewhat  complicated  ore-deposit,  we 
must  confess  that  a  superficial,  tourist's  examination  of  it  could  not 
give  satisfactory  results.  Yet  the  literature  of  this  subject  refers  us 
to  such  materials  chiefly.  Even  treatises  based  upon  the  profound 
studies  of  years  do  not  exhaust  the  subject ;  for  they  are  affected  by 
the  existing  stage  of  development  of  the  auxiliary  sciences,  by  the 
existing  degree  of  exploration  and  exposure  of  the  deposits  de- 
scribed, and  by  the  personal  views  of  their  authors. 

Mining,  indeed,  constantly  furnishes  fresh  evidences  in  new  open- 
ings, but  it  destroys  the  old  at  the  same  time;  and  if  these  are  not 
preserved  for  science  before  it  is  too  late,  they  are  lost  forever.  The 
whole  mining  industry  is  in  its  nature  transitory ;  but  the  nation, 
which  intrusts  to  the  miner,  upon  certain  conditions,  the  extraction 
of  its  mineral  wealth,  has  a  right  to  demand  that  the  knowledge  thus 
gained  at  the  cost  of  a  part  of  the  national  resources  shall  not  be 
lost  to  science. 

PART  I. 
GENERAL  FACTS  AND  THEORIES. 

1.    SYSTEMS  OF  CLASSIFICATION  EMPLOYED  HITHERTO. 

Studies  of  individual  deposits  naturally  involve  speculations 
concerning  their  genesis,  and  many  such  monographs  contain  valu- 
able data,  which,  for  the  more  thoroughly  examined  mining  dis- 
tricts, are  so  well  established  and  so  comprehensive  as  to  invite  a 
systematic  arrangement  and  a  genetic  explanation.  At  first,  only 
the  form  of  the  ore-deposit  was  considered  in  such  classifications ; 
afterwards  the  barren  surrounding  medium  was  included.  From 
this  standpoint,  unfortunately  still  taken  by  some  purely  empirical 
experts,  the  earth's  crust  is  primarily  divided  into  ore-bearing  and 
barren  rocks. 

It  was  especially  the  true  veins,  at  one  time  the  principal  objects 
of  mining,  which  gave  rise  to  speculations  and  discussions,  having 
now  only  a  historic  interest.*  A.  Werner  was  the  first  to  frame  a 
scientific  theory.  He  distinguished  between  ore-deposits  contempo- 
raneous in  origin  with  the  enclosing  rocks  and  those  of  subsequent 

*  The  period  1556  to  1791,  that  is,  from  G.  Agricola  to  A.  Werner,  is  an  illus- 
tration. See  also  Die  Besonderen  Lagerstatten  der  Mineralien,  by  J.  Waldauf  von 
Waldenstein,  Vienna,  1824,  p.  164,  etc. ;  Die  Lehre  von  den  Erzlagerstatten,  by  B.  von 
Cotta,  2d  ed.,  Freiberg,  1859,  p.  85,  and  the  English  translation  by  F.  Prime;  and 
J.  A.  Phillip's  Treatise  on  Ore-Deposits,  London,  1884,  p.  74,  etc. 


4  THE   GENESIS   OF   ORE-DEPOSITS. 

formation,  and  proved  once  for  all  that  veins  are  fissures  filled  with 
ore,  thus  furnishing  the  most  important  characteristic  for  the  rec- 
ognition of  primary  and  secondary  formations.  As  to  the  manner 
in  which  fissures  have  been  filled,  Werner's  theory,  based  upon  a 
comparatively  limited  field  of  observation,  has,  like  many  of  his 
neptunistic  views,  failed  to  maintain  itself;  and  this  question  remains 
still  without  a  final  answer. 

Curiously  enough,  many  systematizers  reproached  Werner  for 
having  introduced  into  his  system  a  genetic  principle,  which  they 
sought  to  eliminate,  confining  themselves  to  the  form  of  deposit  as 
a  guide.  Thus  Waldenstein  (op.  cit.,  p.  5)  distinguished  (a)  tabular 
deposits  (beds  and  veins) ;  (6)  stock-deposits,  flat-lying  or  steeply 
inclined ;  and  (c)  scattered  masses,  such  as  nests  and  pockets. 

Even  Cotta,  otherwise  an  earnest  advocate  of  geological  princi- 
ples, classified  ore-deposits  according  to  their  form  and  kind  as  beds, 
veins  and  masses,  adding  a  new  and  somewhat  indefinite  group  of 
"impregnations."  J.  Grimm*  also  followed  in  the  main  the  old 
principles  of  classification  ;  included  in  his  system  the  eruptive  ore- 
breccias  which  he  had  personally  examined  and  the  tabular  segrega- 
tions of  ore,  and  pronounced  not  only  ore-beds  (Erzlager\  but  also 
certain  bed-masses  (Lagerstocke)  to  be  sedimentary  formations.  Dr. 
A.  von  Groddeckf  followed  genetic  principles  already  acquiring 
predominance.  He  distinguished  :  (a)  original  deposits,  and  (b)  de- 
posits of  debris.  The  former  he  subdivided  into  (1)  those  formed 
contemporaneously  with  the  country-rock,  and  stratified  (ore-beds, 
segregated  beds,  etc.)  or  massive ;  (2)  those  formed  later  (cavity- 
fillings,  veins,  cave-deposits,  metamorphic  deposits).  He  pronounced 
ore-beds  (Erzlager)  to  be  sedimentary,  and  included  in  his  system  the 
cave-deposits  and  metamorphic  deposits  without  describing  their 
occurrence  in  detail.  He  declared  that  his  system,  like  all  others, 
had  only  the  purpose  of  arranging  the  material  of  observation  con- 
veniently for  comprehensive  study,  and  that  the  manifold  products 
of  nature  could  not  be  forced  into  a  system  of  classification. 

Groddeck's  description  of  the  series  of  forms  of  deposits  is  highly 
original.  He  presents  a  number  of  types,  mainly  characterized  by 
the  varying  material  of  the  deposits  and  its  manifold  combinations 
and  transitions.  Evidently  there  was  before  him  the  ideal  of  com- 
bining in  a  systematic  representation  the  different  standpoints  from 
which  the  subject  was  to  be  viewed.  At  least,  if  I  correctly  under- 

*  Die  Lagerstatten  der  nutzbaren  Mineralien,  Prague,  1869. 

t  Die  Lehre  von  den  Lagerstattt-n  der  Erze.     Ein  Zweig  der  Geologie,  Leipzig,  1 879. 


THE   GENESIS   OF   ORE-DEPOSITS.  5 

stood  his  personal,  oral  communication  of  his  views,  he  hoped  to 
represent  one  standpoint  by  abscissae  and  the  other  by  ordinates,  so 
that  the  intersection  would  determine  the  type  of  the  deposit.  This 
is  true  enough ;  but  it  presupposes  an  exhaustive  knowledge  from 
both  standpoints,  which  we  unfortunately  do  not  possess.  My  way 
of  looking  at  the  subject  was,  as  appears  from  his  expressions  in  a 
later  publication,  incomprehensible  to  him.*  It  seemed  to  him  a 
sort  of  heresy  to  doubt  the  contemporaneous  deposition  of  the  ore 
of  the  Mannsfeld  copper-schists  with  the  rock,  although  I  assured 
him  that  this  doubt  need  only  continue  until  the  chemical  and  phy- 
sical possibility  of  such  a  deposition  should  be  shown. 

Groddeck's  system  comprises,  it  is  true,  the  metamorphic  de- 
posits, but  without  special  definition  or  illustrative  examples.  In 
answer  to  a  criticism  of  A.  Stelzner'sf  on  this  point,  he  replies  that 
he  has  included  in  this  class  those  deposits  also  which  have  been 
formed  through  alteration  of  the  rock-material  by  the  process  which 
Stelzner  had  proposed  to  call  metasomasis,  but  that  the  ore-bearing 
masses  thus  originated  cannot  be  regarded  as  separate  deposits,  be- 
cause they  are  only  incidental  phenomena  of  the  filling  of  cavities. 
In  other  words,  he  grants  but  subordinate  rank  to  one  of  the  clearest 
and  most  important  genetic  aids  to  classification,  furnished  by  the 
occurrence  of  rocks  transformed  into  ore.  After  conceding  that  de- 
posits of  debris  should  probably  be  included  among  stratified  de- 
posits, he  restricts  his  system  to  four  chief  classes :  1.  Stratified  or 
sedimentary  deposits;  2.  Massive  or  eruptive  deposits;  3.  Cavity- 
fillings;  4.  Metamorphic  and  raetasomatic  deposits.  This  brings 
him  essentially  nearer  to  my  view,  which  groups  the  first  two  classes 
together,  as  contemporaneous  with  the  country-rock  in  origin,  with 
the  reservation,  however,  that  the  contemporaneity  indicated  by  the 
stratigraphy  should  be  verified  by  other  evidence. 

While  the  work  of  J.  Grimm  comprises  all  useful  deposits,  that 
of  Groddeck  is  confine^  to  ore-deposits,  although  it  would  be  prac- 
ticable to  classify  salt,  coal  and  other  beds  under  his  system. 

In  England  and  America  the  subject  has  been  variously  viewed, 
considerations  of  practice  being  predominant,  and  stratification  being 
regarded  as  the  specially  decisive  factor.  This  conception  appears 

*  "  Beraerknngen  zur  Classifikation  der  Erzlagerstatten,"  Oesterr.  Zeitschr.,  1885  ; 
Rev.  Univ.  des  Mines,  1886,  xix. ;  Gornoj  Jour.,  1886,  iii.,  p.  430.  "  Unverstandlich 
1st  es  mir,  dass  Posepny,  der  sich  so  grosse  Verdienste  urn  die  Kenntnisse  der  Erz- 
lagerstatten erworben  hat,  das  Vorkommen  sedimentarer  Erze  ganz  ignorirt,"  etc. 

t  Cited  in  Dasneue  Jahrb.f.  Mineralogie,  ii.,  1880,  p.  50. 


6  THE   GENESIS   OF   ORE-DEPOSITS. 

first,  so  far  as  I  know,  in  the  writings  of  J.  D.  Whitney,*  who  di 
vides  mineral  deposits  primarily  into  (1)  superficial,   (2)  stratified 
and  (3)  unstratified.     The  stratified  deposits  are  divided   into  (a) 
those  in  which  the  valuable  mineral  constitutes  the  mass  of  a  bed, 

(b)  those  in  which  it  is  disseminated  through  sedimentary  beds,  and 

(c)  those  originally  deposited  from  aqueous  solution,  but  since  meta- 
morphosed.    The  unstratified  deposits  are  again  divided  as  irregular 
[subdivided  into  (a)  masses  of  eruptive  origin    (b)  disseminated  in 
eruptive   rocks;   (c)  stock-work  deposits;    (d)  contact-deposits;  (e) 
fahl bands]  and  regular  [subdivided  as  (/)  segregated   veins;  (g) 
gash-veins;  (h)  true  or  fissure- veins]. 

We  find  here  an  explanation  of  the  term  "  gash-veins,"  unfamiliar 
in  Europe.  Whitney  says  (op.  cit.  p.  225) : 

"  Segregated  veins,  which  are  peculiar  to  the  altered  crystalline,  stratified  or 
metamorphic  rocks,  are  usually  parallel  with  the  stratification  and  not  to  be  de- 
pended on  in  depth.  Gash-veins  may  cross  the  formation  at  any  angle,  but  are  pe- 
culiar to  the  unaltered  sedimentary  rocks.  True  veins  are  aggregations  of  mineral 
matter,  accompanied  by  metalliferous  ores,  within  a  crevice  or  fissure,  which  had 
its  origin  in  some  deep-seated  cause,  and  which  may  be  presumed  to  extend  for  an 
indefinite  distance  downwards." 

Somewhat  different  is  the  classification  of  R.  Pumpelly,f  who 
distinguishes:  I.  Surf  ace- deposits  [(1)  residuary,  (2)  stream-,  (3) 
lake-  and  bog-deposits].  II.  Forms  due  to  the  texture  of  the  en- 
closing rock  or  to  its  mineral  constitution,  or  to  both  [(1)  dissem- 
inated concentrations,  further  subdivided  as  (a)  impregnations  and 
(b)  fahlbands ;  (2)  aggregated  concentrations,  comprising  (a)  lenticu- 
lar, (b)  irregular  masses  or  "  stocks,"  (c)  reticulated  veins  or  "  stock- 
works,"  (d)  contact-deposits].  III.  Forms  due  chiefly  to  pre-existing 
cavities  or  open  fissures  [(1)  cave-deposits ;  (2)  gash-veins ;  (3)  fissure- 
veins]. 

Dr.  R.  W.  Raymond,;);  who  followed,  in  the  main,  the  classifica- 
tion of  Lottner,§  distinguished  :  I.  Superficial  Deposits  [(1)  Deposits 
of  debris  (placers) ;  (2)  surface-formations  in  place  (bog-ore,  etc.)] 
II.  Inclosed  deposits  [(1)  sheet-formed  or  tabular,  divided  into  (a) 

*  Report  of  a  Geological  Survey  of  the  Mississippi  Lead  Region,  Albany,  1868,  p. 
224,  and  The  Metallic  Wealth  of  the  United  States,  Philadelphia,  1854,  p.  34. 

f  Not  possessing  the  original  work,  I  quote  from  the  monograph  of  S.  F.  Ern- 
mons,  Geology  and  Mining  Industry  of  Leadville,  Washington,  1886,  p.  373. 

J  Report  of  the  Commissioner  of  Mining  Statistics,  Washington,  1871,  and  the  re- 
print, Mines  and  Mining  of  the  Rocky  Mountains,  New  York,  1871,  p.  373. 

g  Bergbaukunde,  Berlin,  1878. 


THE   GENESIS   OF   CUE-DEPOSITS.  7 

lodes  or  veins,  and  (b)  beds  and  seams;  (2)  mass-deposits,  divided 
into  (a)  masses,  and  (b)  impregnations,  etc.;  and  (3)  other  irregular 
deposits,  such  as  (a)  pockets  distributed  in  large  deposits,  (b)  isolated 
segregations,  gash- veins,  etc.]. 

Prof.  J.  S.  Newberry*  adheres  mainly  to  the  classification  of  J.  D. 
Whitney,  with  some  new  matter  of  his  own,  the  value  of  which  has 
been  justly  estimated  by  Raymond.f 

An  analogous  line  of  thought  is  followed  by  J.  A.  Phillips.J  He 
declares  that  a  careful  study  of  the  origin,  structure,  and  composi- 
tion of  ore-deposits,  appears  to  justify  their  division  into  the  follow- 
ing groups:  1.  Superficial  [(a)  formed  by  the  mechanical  action  of 
waters, (b)  resulting  from  chemical  action];  2.  Stratified  [(a)  consti- 
tuting the  bulk  of  metalliferous  beds  formed  by  precipitation  from 
aqueous  solution^,  (b)  beds  originally  deposited  from  solution,  but 
subsequently  altered  by  metamorphism,  (c)  ores  disseminated  through 
sedimentary  beds  in  which  they  have  been  chemically  deposited] ; 
(3)  Unstratified  [(a)  true  veins,  (b)  segregated  veins,  (c)  gash  veins, 
(d)  impregnation,  (e)  stock-works,  (/)  fahlbands,  (g)  contact-deposits, 
(h)  chambers  or  pockets]. 

In  France,  comparatively  little  has  been  done  in  framing  such 
systems,  higher  importance  being  attached  to  the  synthesis  of  the 
minerals,  the  explanation  by  experiment  of  geological  processes,  and 
the  attempt  to  confirm  by  the  study  of  mineral-deposits  in  other  coun- 
tries the  theories  thus  supported.  Observations  have  been  made  in 
many  cases,  not  to  furnish  material  for  new  conclusions,  but  to  prove 
the  truth  of  existing  theories,  as,  for  instance,  Elie  de  Beaumont's 
theory  of  "pentagonal  symmetry"  in  the  relation  between  mineral 
veins  and  the  courses  of  mountain  ranges,  etc. 

In  recent  times,  the  chemical  standpoint  has  become  dominant 
with  the  French  school,  and  in  the  treatise  of  De  Launay,§  which 
has  just  appeared,  the  attempt  is,  in  fact,  made  to  base  a  system  of 
ore-deposits  upon  a  purely  chemical  view  of  the  subject.  He  dis- 
tinguishes:  1,  Giles  d'inclusions  (ores  as  primitive  constituents  of 
eruptive  rocks);  2,  GUes  filoniens  (containing  ores  deposited,  no 

*  "  The  Origin  and  Classification  of  Ore- Deposits,"  School  of  Mines  Quarterly, 
New  York,  March,  1880;  also,  Eng.  and  Min.  Journal,  New  York,  vol.  xxix.,  1880, 
pp.  421  and  437. 

f  Eng.  and  Min.  Jour.,  vol.  xxx.,  1880,  p.  1. 

t  "  A  Treatise  on  Ore-Deposits,  London,  1884,  p.  3. 

\  "  Formations  des  Gites  Metalliferes,"  Encyclopedia  Scientifique,des  Aide-memoirts 
publiee  sous  la  direction  de  M.  Leaute,  Paris,  1893. 


8  THE   GENESIS   OF   ORE-DEPOSITS. 

matter  how,  in  pre-existing  cavities  in  the  rocks)  ;  and,  3,  Giles  s6di- 
mentaires  (where  metallic  substances  have  been  laid  down,  either  as 
sediments  or  as  precipitates,  in  marine-  or  fresh-water  basins).  In 
another  place  I  will  say  something  of  this  view,  which,  in  some  re- 
spects, corresponds  with  my  own. 

It  is  evident  from  the  foregoing  mere  enumeration  of  the  names 
of  groups  and  classes  of  the  several  systems  that,  as  a  general  rule, 
every  new  observation,  considered  important  by  the  observer,  haa 
been  added  to  the  established  traditional  conception,  which,  however, 
was  primarily  based  upon  distinctions  of  form  and  kind,  to  which 
genetic  principles,  if  recognized  at  all,  were  secondary.  I  may  re- 
fer, in  illustration,  to  the  class  of  "pipe-veins,"  and  the  exhaustive 
paper  of  Dr.  Raymond*  demolishing  it.  I  myself  once  thought  a 
new  group  to  be  warranted  by  conclusive  observations,  namely, 
typhonic  deposits,!  in  which  the  ores  occur  cementing  together  the 
fragments  of  a  brecciated  mass.  But  I  soon  became  convinced  by 
the  observation  of  other  occurrences,  equally  difficult  to  fit  into  the 
existing  system,  that  the  whole  system  must  be  transformed  before 
it  conld  assimilate,  without  destruction  to  itself,  the  new  facts  ob- 
served in  the  course  of  time. 

But  a  stable  and  complete  system  could  only  be  framed,  when  all 
the  controlling  facts — in  other  words,  all  the  ore-deposits — were  ac- 
curately known.  This  is  not  likely  ever  to  be  the  case.  New  ob- 
servations are  constantly  made  in  mining,  which,  moreover,  often 
obliterates  the  old  ones,  so  that  they  cannot  be  verified  and  com- 
pared. 

It  is,  however,  absolutely  necessary,  in  a  field  so  complicated  as 
that  of  ore-deposits,  to  have  some  general  understanding,  some  sort 
of  system,  comprising  what  is  known.  And  evidently,  in  framing 
a  system,  the  characters  of  form,  being  the  most  obvious  and  the 
most  familiar  to  the  miner,  would  be  naturally  emphasized,  while 
genetic  characters  were  left  in  the  background.  But  this  ought  not 
to  check  genetic  investigation,  or  the  advancing  recognition  of  real 
relation?.  A  genetic  system  must,  indeed,  involve  hypotheses,  and 
may  not,  for  a  while,  be  practically  useful ;  but  in  time  it  will,  like 
every  other  cultivated  branch  of  geology,  assume  more  permanent 
forms. 

At  the  Przibram  Mining  Academy  there  was  established,  in  1879, 

*  Trans.  A.  I.  M.  E.,  vi.,  1887,  p.  393. 

f  "Ueber  typhonische  Gesteinsmassen,"  Verh.  d.  k.  k.  geol     Anstalt,  1871,  p.  94. 


THE    GENESIS   OF   ORE-DEPOSITS.  9 

a  new  chair  of  "  The  Geology  of  Mineral  Deposits/7  which  I  occu- 
pied for  about  ten  years.  As  the  title  indicates,  it  was  not  merely 
intended  for  instruction  in  the  usual  "science  of  mineral  deposits," 
ancl  not  as  a  geological  course,  appended  to  the  technical  course  in 
mining,  as  might  be  inferred  from  a  title  like  "  Montangeologie"  or 
"  Mining  Geology."  The  leading  subject  in  view  was  the  genesis 
of  the  useful  mineral  deposits.  In  the  present  paper  I  purpose  to 
give  a  brief  statement  of  the  substance  of  my  lectures,  which,  apart 
from  a  few  extracts,  have  never  been  published. 

2.  STANDPOINT  AND  VIEW  OF  THE  PRESENT  PAPER. 

The  principal  genetic  distinction  is  doubtless  between  deposits 
contemporaneous  with  the  country-rock,  and  those  subsequently 
formed  in  it. 

The  earth's  crust  consists  of  rock-elements,  chiefly  individualized 
as  mineral  species.  Two  or  three  dozen  of  them — the  rock-forming 
minerals — constitute  by  far  the  larger  part  of  the  solid  earth  as 
known  to  us.  The  remainder,  much  greater  in  number  and  variety, 
ornament  our  mineral  cabinets,  but  form  an  insignificant  portion  of 
the  rocks.  The  greater  part  of  this  group  is  made  up  of  the  legion 
of  minerals  occurring  in  ore-deposits  ;  and  most  of  these  have  un- 
doubtedly had  a  secondary  origin  in  the  rocks — for  instance,  all  the 
cavity-fillings,  which  of  course  could  only  be  deposited  after  the 
rocks  were  formed.  The  secondary  origin  of  some  minerals  which 
do  not  occur  in  cavity-fillings  is  less  evident.  But  they  occur  some- 
times in  company  with  those  which  clearly  have  this  character ;  so 
that  we  may  consider  these  numerous  minerals,  occurring  in  com- 
paratively small  quantities,  as  secondary. 

We  have  two  main  groups  of  mineral  aggregates  :  that  of  the 
rocks,  and  that  which  we  will  call  comprehensively  the  mineral 
deposits.  The  minerals  of  the  first  group  belong  to  it  as  native  and 
original ;  those  of  the  second  are  foreigners  to  the  rocks  in  which 
they  occur.  The  two  groups  may  therefore  be  designated  (from 
?<5coc,  one's  own,  and  £&<>?,  strange)  as  Idiogenous  and  Xenogenous 
respectively. 

It  is  not  necessary  here  to  consider  the  various  origins  of  rocks, 
since  we  take  as  our  starting-point  the  rocks  already  formed.  The 
clearly  sedimentary  rocks  consist  of  the  debris  of  older  formations — 
idiogenous  as  well  as  xenogenous ;  and  we  must  distinguish  in  them, 
besides  mechanical  sediments,  chemical  precipitates  and  organic 
products. 


10  THE   GENESIS   OF   ORE-DEPOSITS. 

The  sediment  of  a  basin  is  the  detritus  carried  into  it  from  the 
land  and  deposited  in  the  form  of  a  flat  wide  cone.  Successive 
conical  envelopes  should  therefore  strictly  be  the  form  of  such  sedi- 
mentary beds,  though  frequently  they  present  apparently  level  par- 
allel strata.  The  deposition  of  a  precipitate,  on  the  other  hand, 
takes  place  throughout  the  liquid  in  the  basin,  and  its  form  more 
completely  represents  the  ideal  stratum.  In  both  sediments  and  pre- 
cipitates, we  find  sometimes,  besides  organic  remains,  finely  divided 
organic  substances,  forming  the  bituminous  portions  of  the  rocks. 
But  the  great  masses  of  vegetable  matter  forming  the  coal-beds  were, 
according  to  the  most  widely  held  opinion,  deposited  in  swampy 
bottoms,  and  are  therefore  neither  sediments  nor  precipitates.  Several 
coal-beds,  one  above  another,  indicate  a  slow  sinking  of  the  basin, 
and  its  periodical  filling-up  with  detritus  from  the  rivers  to  such  an 
extent  that  vegetation  could  again  take  root. 

A  coal-basin  with  several  beds  becomes  on  this  view  the  measure 
of  the  sinking  which  is  doubtless  the  cause  of  every  large  basin, 
but  which  only  becomes  strikingly  evident  when  the  basin  contains 
coal-seams. 

The  foregoing  points  are  mentioned  because  they  indicate  original 
discordances  in  stratification  among  the  sedimentary  layers  them- 
selves, and  between  these  and  the  precipitates  and  organic  forma- 
tions. 

If  we  find  in  the  midst  of  these  formations  ores  lying  exactly 
between  two  strata,  this  relation  is  not  conclusive  proof  of  their 
sedimentary  or  precipitative  origin.  This  must  be  proved  in  every 
given  case  ;  for  in  the  present  state  of  our  knowledge  we  cannot 
understand  how  the  metallic  sulphides  so  characteristic  of  ore-deposits 
could  be  formed  in  that  way. 

As  to  the  eruptive  rocks,  we  do  not  know  what  they  once  were, 
as  we  study  them  only  from  the  moment  of  cooling.  But  we  observe 
at  once  that  iron — a  metal  widely  distributed  in  ore-deposits  and  in 
nature  generally,  occurs  primitive  in  these  rocks,  in  the  form  of 
magnetite,  a  mineral  of  striking  metallic  appearance. 

This  idiogenite  of  the  eruptive  rocks  can  be  detected  without 
chemical  aid;  but  with  such  aid  we  find  traces  of  other  metals  besides 
iron ;  and  this  leads  us  to  surmise  that  the  eruptives  have  brought  a 
whole  series  of  heavy  metals  up  from  the  "  barysphere "  into  our 
"  lithosphere,"  and  that  it  looks  as  if  the  metals  of  our  ore-deposits 
originally  belonged  to  the  barysphere.  This  surmise  De  Launay 
regards  as  already  proved.  He  derives,  as  it  were,  a  priori,  all  the 


THE   GENESIS   OF   ORE-DEPOSITS.  11 

heavy  metals  of  our  ore-deposits  from  the  eruptive  rocks,  and  erects 
upon  this  hypothesis  an  entire  system. 

3.  THE  XENOGENITES  IIST  GENERAL. 

With  relation  to  the  xenogenites  or  mineral  deposits,  the  first 
question  concerns  the  space  which  every  secondary  mineral  or  mineral- 
aggregate  requires  to  establish  its  existence.  It  must  either  have 
found  this  space  waiting  for  it,  or  it  must  have  made  room  by  driv- 
ing out  an  original  mineral. 

Although  we  shall  chiefly  consider  cavities  formed  in  rocks  after 
the  formation  of  the  rocks  themselves,  we  must  not  forget  that  some 
may  have  been  primitive  in  the  rocks.  We  know  that  in  substances 
of  the  greatest  apparent  density  small  cavities  or  pores  must  exist, 
since  we  can,  for  instance,  by  adequate  pressure,  force  quicksilver 
through  them.  Moreover,  we  encounter  in  the  eruptive  rocks  larger 
cavities,  suited  to  receive  considerable  mineral -aggregates — the  so- 
called  blow-holes.  These  phenomena  must  certainly  be  considered, 
although  the  cavities  of  secondary  origin  will  first  be  the  subject  of 
attention. 

With  regard  to  the  filling,  I  observe,  first,  that  the  mineral 
deposits  upon  the  walls  of  cavities,  from  liquids  circulating  within 
them,  usually  have  a  characteristic  structure,  for  which  I  propose 
the  name  "  crustification,"  as  a  companion  to  "stratification." 
(Single  crusts  were  formerly  called  mineral  shells  or  scales ;  and 
Groddeck  introduced  the  word  "  crust,"  which  is  comprehensible  in 
most  languages.) 

Most  frequently  mineral  crusts  occur  concentrically  in  regular 
succession,  and  fill  the  whole  cavity  (except  the  central  druse),  thus 
forming  a  symmetrical  crustification.  They  cover,  however,  not 
only  the  cavity-walls,  but  the  surface  of  every  foreign  body  in  the 
cavity,  thus  forming  crusted  kernels  which  greatly  complicate  the 
phenomenon.  We  shall  see,  however,  that  a  geode-cavity  serves 
much  better  than  a  fissure-cavity  to  explain  the  relations  of  crustifica- 
tion, and  that  the  crusted  kernels  will  give  us  no  trouble  in  that 
regard. 

Sometimes  mineral  crusts  have  undergone  a  secondary  alteration 
(carbonates  are  replaced  with  silica,  etc.).  The  crustification  is  thus 
made  less  distinct,  or  is  even  obliterated.  As  a  general  rule,  how- 
ever, crustification  is  a  characteristic  feature  of  cavity-filling. 

The  cavities  are  formed  either  by  mechanical  or  by  chemical  forces ; 
and  these  two  classes  must  be  sharply  distinguished,  in  view  of  the 


12  THE   GENESIS   OF   ORE-DEPOSITS. 

important  role  of  each.  The  former  may  be  the  effect  of  exterior 
and  foreign  forces,  or  of  such  as  are  interior,  residing  in  the  rook 
itself.  Formerly  I  called  such  spaces  (with  reference  mainly  to  the 
accompanying  fault-phenomena)  u  Spaces  of  Dislocation ;"  but  I 
believe  the  terra  "  Spaces  of  Discission  "  (from  scindere,  to  tear  apart) 
would  be  more  suitable.  The  latter  class  I  formerly  called  "  Spaces 
of  Corrosion  "  (with  reference  to  the  effect  of  the  leaching  and  attack- 
ing liquids);  but  I  would  now  substitute  the  more  self-explanatory 
name  "  Spaces  of  Dissolution." 

Spaces  of  dissolution  naturally  occur  in  soluble  rocks,  espe- 
cially limestone,  and  show,  with  wonderful  clearness,  the  irregular 
course  often  followed  by  underground  waters.  At  and  near  the 
surface,  we  often  find  the  cavity-formations  at  the  contact  of  soluble 
with  insoluble  rocks ;  and  we  may  infer  that  this  relation  affects 
also  the  subterranean  circulation.  Solution  seldom  extends  to  the 
whole  mass  of  the  soluble  rock.  Usually  it  affects  a  part  only,  in 
which  it  forms  more  or  less  irregular  chains  of  cavities,  sometimes 
so  large  that  pieces  of  roof  fall  in,  and  thus  spaces  of  discission  are 
locally  produced.  A  cavity  filled  with  secondary  mineral,  however 
irregular  its  form  may  be,  and  even  though  it  cuts  across  the  strati- 
fication, usually  shows  a  predominant  course,  which  we  are  thus  led 
to  recognize  as  the  channel  of  circulation  of  the  liquid  to  which  we 
owe  the  mineral  deposit. 

As  I  shall  show  later,  we  must  assume  that  the  liquid  which 
formed  the  space  of  dissolution  also  performed  the  filling;  in 
fact,  that  both  processes  were  almost  contemporaneous.  Neverthe- 
less, they  must  not  be  confounded  with  the  metamorphic  processes 
where  the  idiogenite  is  expelled,  atom  by  atom,  by  the  xenogenite; 
for  the  deposits  in  spaces  of  dissolution  show  always  a  distinct  crusti- 
fication,  and  hence  every  single  crust,  at  least,  must  have  found 
free  space  waiting  for  it. 

Concerning  the  origin  of  spaces  of  discission,  so  much  has  been 
written  that  it  cannot  even  be  stated  in  abstract  here.  Two  groups 
of  these  are  distinguished.  Those  of  the  first  group  do  not  extend 
beyond  one  rock,  and  the  force  which  produced  them  probably  has 
its  seat  in  that  rock.  In  the  eruptives,  they  are  usually  deemed 
fissures  of  contraction  ;  in  limes  and  dolomites,  J.  D.  Whitney  called 
them  gash-veins. 

The  cavities  of  the  second  group  extend  out  of  one  rock  into 
another.  The  force  which  produced  them  resided  outside  of  the 
formation.  Considerable  movements  of  one  wall  along  the  other 


THE   GENESIS   OF   OKE-DEPOSITS.  13 

are  often  evident,  whence  the  common  name,  "fissures  of  disloca- 
tion." 

In  a  paper  upon  this  subject*,  about  twenty  years  ago,  I  attempted 
to  show  that  every  fissure,  in  whatever  material,  must  properly  be  a 
fissure  of  dislocation;  that  the  tendency  to  dislocation  (namely,  an 
unequal  tension  in  the  rock),  precedes  the  formation  of  fissures;  and 
that  whenever  the  condition  of  the  rock  permits,  a  dislocation  of  the 
fissure-walls  can  be  always  traced,  even  in  fissures  of  contraction. 

As  to  the  filling  of  spaces  of  discission,  it  must  not  be  supposed 
that  they  represent  throughout  their  entire  length  open  spaces  of 
uniform  width.  The  original  fissure  was  sometimes  closed,  wholly 
or  partially,  by  the  detritus  originating  in  the  friction  of  the  walls, 
or  by  the  movement  or  "swelling"  of  the  country-rock,  or  by  other 
causes.  Only  the  places  remaining  open  would  permit  an  active  cir- 
culation of  solutions  and  a  regular  deposition  from  them.  At  points 
obstructed  there  would  be  no  circulation,  or  a  very  sluggish  one. 
AVhen  high  pressure  was  present,  and  the  rock  contained  interstices, 
the  liquid  doubtless  penetrated  from  the  fissure  into  the  rock,  impreg- 
nating it  with  mineral ;  or  a  soluble  rock  was  attacked,  and  spaces 
of  dissolution  were  formed,  to  be  filled  in  like  manner  as  the  tissure 
itself. 

This  explains  the  fact  that,  on  the  same  vein-plane,  rich  deposits 
alternate  with  poor  or  barren  spots,  and  that  the  miner,  seeking  a 
bonanza,  persistently  follows  the  barren  traces  of  the  vein,  according 
to  a  well-known,  fundamental  law  of  prospecting. 

From  the  genetic  standpoint,  the  richer  portions  are  interesting  as 
sometimes  occupying  more  or  less  regular  belts  in  the  vein-plane, 
called  "channels,"  "shoots,"  "chimneys,"  etc.  These  names  evi- 
dently designate  the  main  channels  through  which  the  mineral  solu- 
tions passed ;  and  the  occurrence  of  such  forms  in  most  kinds  of 
deposits  tends  to  prove  that,  notwithstanding  other  differences,  they 
were  all  formed  in  a  similar  way. 

The  primitive  rock-cavities  (pores  and  blow-holes)  may  also  be 
filled  with  secondary  minerals.  In  the  former,  there  results  a  finely 
disseminated  mineral  substance,  constituting  such  a  deposit  as  Cotta 
denominated  impregnation.  Blow-holes  are  very  often  filled  with 
minerals  of  the  quartz  family  (opal,  chalcedony,  etc.),  and  we  are  often 
able  to  infer  from  the  structure  of  such  geodes  the  process  by  which 
they  were  filled. 

*  "  Geol.  Betrachtungen  iiber  die  Gangspalten,"  Jahrb.  d.  k.  k.  Bergakademien, 
xxii.,  Vienna,  1874. 


14  THE   GENESIS   OF   ORE-DEPOSITS. 

Where  the  mineral  solutions  found  no  cavity  already  prepared, 
they  must  have  conquered  the  necessary  place  by  expelling  a  corre- 
sponding part  of  the  original  material.  When  one  mineral  indi- 
vidual was  replaced  by  another,* as  in  cases  of  pseudornorphs,  the 
nature  of  the  process  can  often  be  inferred  from  a  comparison  of  the 
composition  of  the  two;  and  the  laws  thus  discovered  may  frequently 
be  applied  to  the  problems  of  the  origin  of  mineral  aggregates. 
Many  phenomena,  however,  even  in  the  formation  of  pseudo- 
morphs,  are  hard  to  explain, — the  fact,  for  instance,  that  in  some 
minerals  the  change  commences  within  the  mass  and  progresses  out- 
ward, etc. 

Where  the  original  material  was  expelled,  there  must  have  been 
first  an  access  for  the  liquids  which  began  and  executed  this  effect. 
Such  may  be  furnished  by  original  minute  rock-cavities,  or  by  sec- 
ondary cavities. 

The  original  substance  of  the  greater  part  of  the  pseudornorphs 
known  to  us  was  composed  of  soluble  minerals,  such  as  carbonates, 
sulphates,  and  chlorides,  which  also  occur  as  the  elements  of  rocks. 
Hence  it  may  be  inferred  that  metamorphous  or  metasomatic  de- 
posits will  be  especially  frequent  in  soluble  rocks  like  limestone, 
dolomite,  etc.,  and  that  we  may  also  expect  such  deposits  to  occur 
frequently  in  company  with  those  which  fill  spaces  of  dissolution. 

Pseudomorphs  show  us  one  substance  in  the  crystal-form  of  an- 
other. This  indication  is  lacking  for  the  recognition  of  metaso- 
matic deposits ;  yet  sometimes  the  original  rock  was  characterized 
by  peculiar  structure,  such  as  lamination  or  jointing — as,  for  instance, 
the  cellular  structure  of  the  Rauckwacke  (Cargneule),  which  is  re- 
produced in  the  cellular  calamine  which  has  replaced  it.  Moreover, 
the  original  rock  may  have  contained  fossils,  which  have  been  re- 
placed, with  the  rest,  by  the  new  mineral,  retaining  their  form;  for 
instance,  the  bivalves  and  mollusks  of  the  Bleiberg  limestone  in 
Carinthia  and  at  Wiesloch  in  Baden,  reproduced  in  galena  and 
calamine;  the  brachiopods  of  the  Silurian  iron-ores  of  central  Bohe- 
mia, etc. 

Most  important  for  the  study  of  the  process  are  transitional 
forms  between  the  earlier  and  the  later  material ;  for  instance,  coat- 
ings of  the  latter  upon  kernels  of  the  former,  such  as  limonite  upon 
siderite  or  ankerite;  and  likewise  important  is  the  occurrence  of 
regular  pseudomorphs,  replacing  one  element  in  a  heterogeneous 
rock,  like  those  of  cassiterite  after  feldspar  in  the  granite  of  Corn- 
wall. 


THE   GENESIS   OF   OEE-DEPOSITS.  15 

After  the  expulsion,  atom  by  atom,  of  the  original  material,  the 
resulting  deposit  must  be  massive,  showing  no  crustification. 

Frequently,  however,  there  are  only  negative  indications  of  the 
metamorphosis.  It  can  be  seen  merely  that  the  deposit  is  not  an 
original  rock;  that  it  has  not  been  deposited  in  pre-existing  primi- 
tive or  secondary  cavities;  and  hence,  that  it  must  have  been  formed 
by  replacement. 

In  general,  two  kinds  of  metamorphous  deposits  may  be  distin- 
guished. In  the  first,  the  new  material  has  replaced  the  more  solu- 
ble ingredients  of  a  heterogeneous  rock,  and  the  result  resembles 
the  description  of  an  impregnation,  in  which  the  new  material  occu- 
pies the  original  interstices  of  the  rock.  In  the  second,  a  part  or 
the  whole  of  a  homogeneous  rock  has  suffered  metamorphosis,  and 
the  deposit  will  bear  a  certain  resemblance  to  filled  cavities  of  dis- 
solution. 

As  I  have  shown  above,  and  will  illustrate  further  on  with  some 
examples,  we  may  thus  establish  certain  types  of  deposits  entirely 
without  reference  to  form.  Some  of  these  may  coincide  with  groups 
in  earlier  systems,  but  others  appear  together  in  one  and  the  same 
group.  This  seems  at  first  not  to  favor  the  practical  usefulness  of 
the  above  principles,  but,  as  I  have  said,  we  do  not  yet  know  enough 
to  frame  a  final  system.  That  must  be  the  aim  of  future  studies, 
and  it  is  obvious  that  our  purely  genetical  factors  will  be  more  help- 
ful than  the  arbitrary  characters  based  upon  the  exterior  form  of 
deposits.  We  distinguish,  then,  Idiogenites,  or  deposits  contempora- 
neous in  origin  with  the  rock,  from  Xenogenites,  the  deposits  of  later 
origin,  including  not  merely  those  of  ores,  but  mineral  deposits  in 
general ;  and  to  these  we  may  add,  in  harmony  with  some  older  sys- 
tems, the  deposits  of  debris  as  a  third  class,  Hysterogenites,  or  latest 
formations. 

The  Xenogenites  we  divide  into  such  as  penetrated  pre-existing 
cavities  (filling  primitive  cavities,  spaces  of  discission,  or  spaces  of  dis- 
solution), and  the  metamorphic  or  metasomatic  dejJbsits,  which  made 
room  for  themselves  by  the  expulsion  of  an  earlier  material. 

The  form  of  all  these  deposits  is  not  fixed,  but  depends  upon  vari- 
ous geological  relations  of  the  country-rock.  The  mention,  under 
former  systems,  of  regular  forms  of  deposit,  contemplated  rather  the 
ideal  of  the  system  itself.  In  reality,  the  ore-bodies  in  "  veins"  and 
"  beds  "  are  irregular,  and  form  masses  for  which  the  most  various 
names  exist  in  all  countries. 


16  THE   GENESIS  OF   ORE-DEPOSITS. 

We  must  now  speak  more  particularly  concerning  the  method  of 
formation  of  the  different  deposits.  Probably  no  one  doubts  at  the 
present  day  that  they  are  predominantly  the  result  of  humid  pro- 
cesses of  solution  and  deposition.  But  such  generalities  are  not 
enough.  The  processes  alleged  must  be  put  upon  the  basis  of 
actual  causes,  still  operative,  and  capable  of  being  proposed  and 
discussed  in  explanation  of  geological  phenomena.  It  is,  there- 
fore, necessary  to  introduce,  at  this  point,  the  theoretical  chapter 
which  follows. 

4.  THE  SUBTERRANEAN  WATER- CIRCULATION. 

In  treating  of  the  genesis  of  mineral  deposits,  this  department 
cannot  well  be  so  lightly  handled  as  it  is  in  most  text-books  of  gen- 
eral geology.  Prof.  A.  Daubree,  in  an  authoritative  discussion  of 
the  subject,*  ascribes  the  mineral  deposits,  among  other  effects,  di- 
rectly to  the  liquids  circulating  underground.  It  is  my  desire,  with 
the  aid  of  personal  observations  incidental  to  my  continuous  study 
of  such  deposits,  to  present  a  somewhat  closer  view  than  that  of 
Prof.  Daubree. 

Surface  phenomena  exhibit  clearly  a  constant  circulation  of 
liquids,  and  corresponding  phenomena,  so  far  as  they  are  observable 
underground,  indicate  the  persistence  of  this  condition,  so  that  we 
must  infer  a  subterranean  circulation  connected  with  that  of  the 
surface.  We  have  then  to  consider,  first,  the  surface-phenomena, 
so  far  as  they  concern  our  purpose,  and,  second,  the  underground 
phenomena. 

As  to  the  former,  we  know  that  it  is  chiefly  the  solar  energy  which 
initiates  the  circulation  by  lifting  above  the  land  the  water  of  the 
sea,  and  thereby  imparting  to  it  the  potential  energy  which  is  vari- 
ously exhibited  in  its  return  to  the  sea.  The  mechanical  effects  of 
flowing  waterf  in  erosion,  transportation,  and  sedimentation  need 
not  occupy  us  here.  As  to  the  chemical  effects,  we  know  that  the 
mineral  constituents  of  the  rocks,  dissolved  through  this  circulation, 
chiefly  find  their  way  in  the  rivers  to  the  sea.  In  regions  without 
drainage  to  the  ocean,  the  dissolved  minerals  are  concentrated  by 
evaporation,  which  may  lead  to  precipitation.  I  would  remark, 
however,  that  in  my  opinion  small  proportions  of  salts  are  me- 

*  Les  eaux  souterraines  a  Fepoque  actuelh,  etc.,  vols.  i.  and  ii ,  Paris,  1887  ;  and  Les 
eavx  souterraines  aux  epoques  anciennes,  etc.,  Paris,  1887. 

f  Die  Wasserfdlle  des  Niagara  und  ihre  geoloyisehe  Bedeutung,  by  F.  Posepny, 
Vienna,  1879. 


THE   GENESIS    OF   ORE-DEPOSIT^.  17 

chanically  taken  up  in  the  evaporation  of  sea-water,*  as  careful 
analyses  of  rain-water  have  proved,  and  that  this  fact  leads  to  the 
explanation  of  the  salt  and  salt  lakes  in  regions  without  drain- 
age, etc. 

A.   The  Vadose  Underground   Circulation. 

In  connection  with  the  underground  phenomena,  the  ground-water 
has  for  us  a  special  interest.  As  is  well-known,  a  portion  of  the 
atmospheric  precipitate  sinks,  through  open  fissures  or  through  the 
pores  of  permeable  masses,  into  the  rocks,  and  fills  them  up  to  a  cer- 
tain level.  When  in  a  given  terrain,  by  wells  or  other  openings,  the 
ground-water  (that  is,  the  water-level,  Grundwasserspiegel,  nappe 
d'eau)  has  been  reached  at  several  points,  it  is  found  that  these  points 
are  in  a  gently  inclined  plane,  dipping  towards  the  deepest  point  of 
the  surface  of  the  region,  or  towards  a  point  where  an  impermeable 
rock  outcrops.  The  ground-water  is  not  stagnant,  but  moves,  though 
with  relative  slowness,  according  to  the  difference  in  height  and  the 
size  of  the  insterstitial  spaces,  down  the  plane  mentioned,  and 
finds  its  way,  in  the  first  instance,  directly  into  the  nearest  surface- 
stream,  or,  in  the  second  instance,  forms  a  spring,  which  takes  indi- 
rectly a  similar  course.  Thus  stated,  free  from  all  complications,  the 
phenomenon  exhibits  clearly  the  law  of  circulation.  The  atmospheric 
moisture  evidently  descends ;  and  even  the  movement  of  the  upper 
layer  of  the  ground- water  is  only  apparently  lateral,  but  really 
downwards,  and  is  determined  (for  equal  sectional  areas  of  the  rock- 
insterstices)  by  the  difference  in  height  between  the  water-level  and 
the  surface-outlet. 

For  that  part  of  the  subterranean  circulation,  bounded  by  the 
water-level,  and  called  the  vadose  or  shallow  underground  circula- 
tion, the  law  of  a  descending  movement  holds  good  in  all  cases,  even 
in  those  complicated  ones  which  show  ascending  currents  in  parts. 
The  total  difference  in  altitude  between  the  water-level  and  the  sur- 
face-outlet is  always  the  controlling  factor. 

When  these  two  controlling  levels  are  artificially  changed,  as  often 
happens  in  mining,  the  law  still  operates.  In  sinking  a  shaft  through 
permeable  ground,  it  is  of  course  necessary  to  lift  continuously  the 
ground-water.  The  water-level  thus  acquires  an  inclination  towards 
the  shaft,  which  may  thus  receive  not  only  the  flow  of  the  immedi- 
ate vicinity  but  even  also  that  of  neighboring  valley-systems.  A 

*  *'  Znr  Genesis  der  Salzablagerungen,   besonders  Jener   im    Amerikanischen 
Westen,"  Sitz.  Ber.  der  k.  k.  Acad.  d.  W.  im  Wien,  1877. 


18  THE   GENESIS   OF   ORE-DEPOSITS. 

shaft  imparts  to  the  previously  plane  water-level  a  depression,  giving 
it  the  form  of  an  inverted  conoid  with  parabolic  generatrix.  An 
adit  produces  a  prismatic  depression  in  the  water-level ;  and  so  on 
for  other  excavations.  On  the  other  hand,  a  bore- hole,  from  which 
the  water  is  not  removed,  does  not  affect  the  water-level. 

Atmospheric  waters  falling  upon  impermeable  rocks  at  the  sur- 
face cannot  penetrate  them,  but  must  join  the  existing  surface-circu- 
lation. The  rocks  are  usually  covered  with  more  or  less  detritus,  in 
the  interstices  of  which  the  ground-water  can  move;  and  the  water- 
level  is  in  most  cases  at  the  boundary  between  the  permeable  surface- 
formation  and  the  impermeable  rock  below. 

These  relations  are  complicated  by  the  occurrence  of  fissures 
(which  the  ground-water  of  course  fills),  and  by  the  communication 
of  such  fissures  in  depth  with  permeable  formations,  which  come  to 
the  surface  somewhere  at  a  lower  level,  though  at  great  distance. 
In  such  cases,  as  is  well  known,  a  siphon-action  is  set  up,  and  the 
ground-water  of  one  region  may  find  an  outlet  far  away,  even  be- 
yond a  mountain  range. 

Peculiar  conditions  are  created  by  the  occurrence  of  relatively 
soluble  rocks,  such  as  rock-salt,  gypsum,  limestone  and  dolomite,  in 
which,  by  the  penetration  of  meteoric  waters  and  the  circulation  of 
the  ground-water,  connected  cavities  are  formed,  constituting  com- 
plete channels  for  the  vadose  circulation. 

It  is  often  possible  to  observe  directly,  not  only  the  formation  but 
also  the  filling  of  these  cavities,  and  thus  to  obtain  valuable  material 
for  the  explanation  of  the  origin  of  xenogenites  outside  the  vadose 
circulation,  and  not  observable  in  the  stages  of  formation. 

It  is  for  our  purpose  a  most  valuable  fact,  that  the  phenomena  of 
leaching  indicate  the  path  of  the  circulating  liquids  through  soluble 
rocks,  so  that  we  can  study  the  process  in  its  several  stages.  The 
water  flowing  at  the  bottom  of  a  cave  in  limestone  is  unquestionably 
ground-water  ;  and  it  follows  that  the  whole  complex  group  of  cavi- 
ties has  been  eaten  out  by  it.  If  in  another  limestone  cave  we  see 
no  flowing  water,  the  current  must  have  found  some  lower  outlet; 
and  the  cave  represents  for  us  an  ancient  ground-water  channel. 

The  many  and  various  phenomena  of  the  Karst  region  are  well 
known :  the  Dolins,  Ponors  and  Katravons — points  where  a  surface- 
stream  sinks  into  the  earth  ;  vertical  openings,  at  the  bottom  of 
which  flow  subterranean  streams ;  and  caves  out  of  which  streams 
issue— illustrating  the  whole  series  of  the  entrance,  the  course  and 
the  exit  of  subterranean  waters. 


THE   GENESIS   OF   ORE-DEPOSITS.  19 

In  1864, 1  had  opportunity  to  observe,  at  Maros  Ujvar,  in  Tran- 
sylvania, a  very  instructive  illustration  of  this  kind,  which  is  shown 
in  Fig.  1.  Here  the  rock-salt  comes  to  the  surface  with  steep  zigzag 
stratification,  and  is  covered  only  with  detritus,  to  the  depth  of  a  few 
meters.*  Mining  is  carried  on  in  great  parallelopiped-shaped 
chambers,  by  means  first  of  levels  run  horizontally  from  a  shaft,  and 
winzes  sunk  vertically  from  these.  The  workings  were  at  that  time 
125  meters  or  400  feet  deep.  A  great  difficulty  in  the  extraction 
was  the  entrance  of  saturated  brine  from  that  side  of  the  mine  where 
the  Maros  river  flowed  by.  Until  the  mine  had  been  protected  by 
an  adit  of  semi-circular  course  in  the  impermeable  rock,  surrounding 
the  salt-body,  the  water  annually  raised  and  delivered  without  utili- 
zation into  the  river  contained  84,000  tons  of  salt,  or  more  than 
twice  the  weight  of  the  rock-salt  mined. 

Various  investigations  have  proved  that  the  water  of  the  river 
passes  through  the  overlying  detritus  to  the  salt-body,  which  it  pene- 
trates at  the  boundary  of  the  impermeable  rock  of  the  hanging-wall, 
finding  its  way  through  separate  channels  to  appear  as  saturated  brine, 
at  the  deepest  point  of  the  mine-workings.  These  channels  had 
most  frequently  a  cylindrical  shape,  smooth  walls,  and  sometimes  so 
great  a  diameter  that  a  man  could  crawl  in.  There  were  always 
several  to  be  seen,  of  which,  of  course,  only  the  lowest  in  position 
brought  the  brine. 

The  explanation  is  simple.  The  water  from  the  river,  reaching 
the  salt-body  through  the  detritus  cover,  acted  at  the  border  of  the 
salt,  where  the  principal  depressions  in  the  surface  were  located,  and 
the  saturated  brine  thus  formed  filled  all  insterstices  in  the  adjoining 
salt-body.  By  the  leaching  of  such  solutions  into  each  deeper  level 
opened  in  the  mine,  a  line  of  maximum  activity  of  circulation  was 
gradually  formed,  which  was  followed  also  by  solutions  not  yet  satu- 
rated, with  additional  leaching  and  the  final  creation  of  open  chan- 
nels as  the  result. 

An  example  on  a  large  scale  of  such  a  channel  in  rock-salt,  crea- 
ted, however,  without  the  aid  of  mining  operations,  was  recently 
described  by  H.  Winklehner,f  who  found  among  other  striking  phe- 
nomena of  lixiviation  in  the  rock-salt  of  the  islands  of  the  Persian 
Gulf,  a  horizontal  natural  channel  or  adit,  on  the  island  of  Larak, 

*  "Studien  aus  dem  Salinargebiete  Siebenbiirgens,"  by  F.  Posepny,  Jahrb.  der 
k.  k.  geol.  Reichsanst.,  1867,  xviii,,  p.  506-516. 

f  "  Salzvorkomraen  in  Siid-Persien,"  Oesierr.  Z.  fur  Berg-und  Huttenwesen,  1892, 
xl ,  p.  581. 


20  THE   GENESIS   OF   ORE- DEPOSITS. 

which  he  was  able  to  follow  for  about  1J  kilom.  (1  mile).  It 
expanded  in  places  to  caverns  12  m.  (39  feet)  high,  without  ever 
extending  outside  of  the  salt. 

In  precisely  the  same  way  were  formed  the  channels  in  other  less 
soluble  rocks,  such  as  limestone,  when,  the  level  of  the  entrance 
being  above  that  of  the  exit  of  the  ground-water,  a  line  of  maximum 
activity  of  circulation  was  established  between  the  two  points.  This 
line,  and  the  cavities  developed  along  it,  would  not,  indeed,  always 
have  the  regular  parabolic  course,  but  would  be  dependent  upon 
various  influences  of  the  stratification,  the  presence  of  rocks  of 
unequal  solubility,  or  even  an  intermixture  of  impermeable  rocks. 
A  mass  of  the  latter,  occurring  on  the  line  connecting  the  two  points 
named,  might  cause  the  channel  to  bend  up  and  down,  or  even  in 
places  to  assume  an  upward  inclination. 

Figs.  2  and  3  illustrate  these  conditions.  S  is  the  soluble,  I  the 
impermeable  rock;  a,  the  entrance-point  and  z  the  outlet-point  of  the 
ground-water;  ab  cz,  the  line  along  which  approximately  a  channel 
might  be  made,  if  the  impermeable  rock  were  not  present.  In  its 
presence,  the  dissolving  current  must  take  another  road,  adz,  follow- 
ing more  or  less  the  contact  between  S  and  I,  and  in  Fig.  2,  de- 
scending to  a  depth  proportioned  to  the  relation  betsveen  the  original 
rock -interstices  and  the  hydrostatic  head,  while  in  Fig.  3  it  first  sur- 
mounts the  dam  formed  by  the  impermeable  rock,  and  then  plunges 
towards  the  outlet  z.  We  see  that  in  this  way  various  channels  may 
originate  at  the  contact  of  permeable  and  impermeable  rocks,  as  in- 
deed we  find  them  often  in  nature. 

But  when  to  these  factors  fissures  are  added,  the  conditions  are 
essentially  changed,  for  the  circulation  follows  in  preference  the  open 
fissures,  and,  if  they  pass  through  soluble  rocks,  enlarges  them  by 
solution. 

Sometimes  the  position  and  the  level  of  the  outlet  are  altered — as, 
for  instance,  in  the  progressive  erosion  of  valleys;  and  it  may  then 
easily  happen  that  the  new  channel,  representing  the  new  conditions, 
will  take  a  totally  different  direction,  crossing  the  line  of  the  old 
one. 

Siphon-action  is  to  be  observed  in  soluble,  much  more  frequently 
than  in  permeable  rocks,  as  the  frequency  of  intermittent  springs  in 
limestone  indicates.  Such  springs  presuppose  the  existence  of  a 
siphon-like  channel,  through  which  the  ground-water  cannot  flow  to 
escape  from  the  lower  leg  until  the  water-level  has  risen  to  the  top  of 
the  bend  of  the  siphon. 


THE    GENESIS    OF   ORE-DEPOSITS.  21 

We  have  seen  that  the  ground-water  may  traverse  deep  fissures 
leading  to  soluble  or  permeable  rocks,  and  may  follow  such  rocks 
for  considerable  distances.  When  the  ground-water,  warmed  in 
depth,  has  an  opportunity  to  reach  the  surface,  such  as  is  given  in 
Fig.  6  by  the  difference,  H,  in  level,  a  thermal  spring  is  the  result — 
a  so-called  acrotherm,  if  its  water  is  not  highly  charged  with  mine- 
rals, and  not  unlike  the  ground-water  of  the  place. 

Artesian  wells  present  an  analogous  case,  also  explained  hitherto 
by  the  principle  of  hydrostatic  pressure  (see  Fig.  7).  The  outcrop 
of  the  permeable  layer  has  been  assumed  to  be  necessarily  higher 
than  the  mouth  of  the  well,  in  order  to  account  for  the  rising  of  the 
water  above  the  latter  level.  The  cause  has  been  conceived  as  the 
operation  of  communicating  pipes,  the  drill  hole  being  one  leg,  and 
the  permeable  layer  the  other,  and  it  has  been  overlooked,  that  the 
latter  is  no  open  pipe,  but  a  congeries  of  rock-interstices,  in  which 
the  water  has  to  overcome  a  great  resistance,  and  that,  perhaps,  in  level 
regions  no  hydrostatic  head  at  all  can  be  demonstrated.  Certainly 
the  powerful  factor  of  the  higher  temperature,  and  in  some  cases  the 
gaseous  contents,  of  the  ascending  water,  were  omitted  from  the  cal- 
culation. 

It  would  be  a  matter  of  surprise  to  me,  if  the  purely  hydrostatic 
and  strictly  mathematical  views  heretofore  current  on  this  subject 
had  not  led  to  disappointment.  I  introduce  Fig.  7,  the  conventional 
diagram  of  an  artesian  well,  for  the  purpose  of  stimulating  further 
thought  on  the  matter. 

The  Filling  of  the  Open  Spaces  Formed  by  the  Vadose  Circu- 
lation.— This  is  very  important  geneticallv,  since  it  is  a  matter  sub- 
ject to  current  and  direct  observation,  and  capable  of  furnishing 
many  conclusions  applicable  to  inaccessible  subterranean  occur- 
rences. 

We  can  observe  spaces  on  the  bottom  of  which,  frequently,  the 
ground-water  which  excavated  them  is  still  flowing,  and  which  are 
therefore  filled  for  the  most  part  with  air.  Liquids  carrying  vari- 
ous minerals  drip  into  these  spaces  and  leave  a  part  of  their  contents 
on  the  walls ;  the  cause  of  deposition  being,  on  the  one  hand,  the 
evaporation  of  a  part  of  the  liquid,  or,  on  the  other  hand,  such 
changes  as  the  loss  of  carbonic  acid,  precipitating  as  carbonate  the 
soluble  bicarbonate  of  lime;  the  oxidation  of  soluble  ferrous  to  in- 
soluble ferric  oxide;  the  reduction  of  ferrous  sulphate  by  organic 
matter  to  sulphide,  etc.  The  form  and  structure  of  these  precipi- 
tates vary  at  different  parts  of  the  walls.  On  the  roof  occur  the 


22  THE   GENESIS   OF   ORE-DEPOSITS. 

stalactites,  and  on  the  floor  (if  it  be  not  covered  with  water)  the  cor- 
responding stalagmites.  The  wall-deposits  have  characteristic  forms 
likewise  ;  so  that  we  can  recognize  by  the  appearance  of  any  piece  of 
the  deposited  mineral  the  place  where  it  was  formed.  But  from 
water  covering  the  bottom  of  the  cavity  only  horizontal  deposits  can 
originate.  Sometimes  the  cavity  is  contracted,  so  that  its  whole 
cross-section  is  occupied  by  the  liquid.  If  it  is  accessible  to  obser- 
vation, we  can  then  see  that  the  deposits  from  the  circulating  liquid 
cover  the  walls  uniformly. 

This  can  be  much  more  clearly  observed  in  artificial  conduits, 
where  precipitation  occurs.  We  find,  for  instance,  in  the  pipes  which 
convey  concentrated  brine,  the  walls  uniformly  covered  with  a  de- 
posit, mostly  of  gypsum.  But  if  air  or  gas  is  admitted  into  the 
pipes,  the  deposit  occurs  only  at  the  bottom.  We  may  thence  infer 
that  so  long  as  the  circulating  liquid  fills  the  whole  cavity  the  attrac- 
tion of  the  walls  for  the  precipitated  particles  is  controlling ;  but  that 
when  gas  enters,  gravity  becomes  predominant  and  draws  these  par- 
ticles to  the  bottom. 

In  opal  and  chalcedony  geodes  we  can  often  see  both  forms  of  pre- 
cipitate :  the  crust  uniformly  covering  the  walls,  and  the  horizontal 
deposit.  Fig.  4  represents  a  geode  of  iron  opal,  from  Dreiwasser, 
in  Hungary,  in  which,  besides  the  crustification  and  horizontal 
deposit,  stalactitic  and  stalagmitic  forms  also  appear.  A  thin  crust 
of  translucent  hyalite  covers  all  parts  of  the  wall,  including  the 
floor.  The  cylindrical  stalactites  are  also  of  hyalite.  Some  of 
them  extend  to  the  bottom,  and  are  perhaps  joined  to  stalagmites 
rising  from  the  crust  there.  The  remaining  space  is  half  filled  with 
a  milk-white,  opaque,  opaline  substance,  in  which  occurs  a  thin 
layer  of  translucent  hyalite.  On  the  same  specimen  several  other 
less  regular  cavities  are  visible.  All  of  them  were  lined  with  the 
hyalite  crust,  and  some  have  also  the  opaline  layers.  These  layers 
are  parallel  in  all  the  cavities ;  and  it  cannot  be  doubted  that  they 
were  horizontally  deposited.  The  stalagmites  stand  at  right  angles 
to  them,  and  were  unquestionably  vertical  when  formed.  The  geode 
certainly  occupied,  therefore,  at  the  place  of  formation,  the  position 
shown  in  Fig.  4. 

I  must  resist  the  temptation  to  describe  the  manifold  forms  of  de- 
posit in  limestone  caves.  Fig.  5,  an  ideal  diagram,  showing  a  wall- 
accretion,  and  stalactites  and  stalagmites,  separate  and  grown  to- 
gether, is  given,  not  to  illustrate  the  variety  of  the  phenomena,  but 
to  indicate  their  analogy  with  those  of  the  little  geode  in  the  iron- 


THE   GENESIS   OF   ORE-DEPOSITS.  23 

opal  of  Fig.  4.  It  is  easy  to  conceive,  that,  under  some  circum- 
stances, particularly  in  old  cavities,  lying  above  the  water-level  and 
not  subject  to  further  enlargement,  the  formation  of  stalactites,  etc., 
might  ultimately  fill  the  whole  space. 

The  floor  of  caves  often  shows  deposits  colored  with  ferric  oxide, 
the  explanation  of  which  is  obvious.  Sometimes  we  find  in  the 
upper  caves  traces  of  sediments  also;  and,  in  one  instance  I  found 
in  an  outlet-cave  pebbles  of  very  hard  rocks,  which  certainly  came 
from  the  surface.*  The  chemical  reaction  of  the  formation  and 
filling  of  these  caves  are  so  simple  as  to  need  no  discussion  here. 

Much  more  various  observations,  however,  can  be  made  in  the 
artificial  caves,  formed  by  mine-workings.  Here  we  have  conditions 
analogous  to  those  of  the  natural  caves,  but  much  greater  variety, 
since  the  most  widely  different  substances  come  into  play.  The 
mine- workings  are  situated  at  an  artificially  depressed  water-level, 
and  will  show,  in  general,  processes  analogous  to  those  observed  in 
limestone  caves,  particularly  the  formation  of  stalactites.  From  cal- 
careous rocks,  from  mineral  deposits,  and  from  the  mine-masonry, 
crusts,  stalactites  and  sinter  are  formed,  analogous  to  those  which  oc- 
cur in  cavities  at  the  natural  water-level.  Processes  of  oxidation 
will  here  also  play  the  leading  part,  although  reduction  may  also  be 
effected  through  the  more  abundant  organic  matter  in  the  mine- 
waters.  Thus  stalactites  of  pyrites,  evidently  reduced  from  ferrous 
sulphate  by  organic  matter,  are  often  found  in  metal-mines.  A 
respectably  large  number  of  observations  already  illustrates  the  pro- 
cesses which  are  going  on  under  our  eyes  in  mines,  and  from  which 
we  can  draw  conclusions  as  to  the  destruction  and  creation  of  many 
minerals  by  circulating  under-ground  solutions.  But  we  must  not 
forget  that  these  proofs  apply  only  to  the  conditions  of  the  shallow 
or  vadose  circulation,  and  that,  for  the  explanation  of  the  formation 
of  the  more  ancient  deposits,  we  must  look  to  the  rock-regions  be- 
low the  water-level. 

In  order  to  give  at  least  one  American  example,  I  refer  to  the 
observation  of  Raymond,  who  found  in  an  old  Spanish  mine,  in  the 
Cerillos  range  of  New  Mexico,  an  iron  pick-axe,  the  eye  of  which  was 
filled  with  beautifully  crystallized  galena,  evidently  a  reduction  of 
lead  sulphate  by  the  decaying  wood  of  the  handle  of  the  pick.f 

It  may  be  said,  in  general,  that  the  results  of  the  processes  of 

*  "Geol.  raont.  Studie  der  Erzlagerstatten  von  R6zbanya  in  S.  O.  Ungarn,"  von 
F.  Posepny,   Ung.  geol.  Gesellsch.,  1874,  p.  48. 
f  Trans.  A.  I.  M.  K,  1883,  xi.,  p.  120. 


.24  THE   GENESIS   OF   ORE-DEPOSITS. 

oxidation,  chlorination,  and  reduction,  observed  in  those  regions  of 
ore-deposit  which  lie  above  water-level,  have  come  to  pass  under 
conditions  analogous  to  those  just  described  ;  so  that  we  are  able  to 
adduce  extended  series  of  proofs,  not  only  as  to  formations  now  going 
on,  but  also  as  to  similar  formations  long  since  finished. 

B.  Ihe  Deep  Underground  Circulation. 

Thus  far,  we  have  considered  only  such  processes  as  take  place  in 
the  region  above  water-level,  and  are  still,  in  some  cases,  open  to 
our  observation.  As  we  descend  to  a  deeper  region,  there  is  less 
hope  of  encountering  formative  processes  still  active.  When  we 
penetrate  by  mining  into  the  depths,  we  artificially  depress  the  water- 
level,  and  create  conditions  unlike  those  which  attended  the  forma- 
tion of  the  deposits. 

But,  if  we  compare  the  deposits  formed  below  water-level,  under 
proportionally  greater  pressure  and  at  higher  temperature,  with  those 
of  the  upper  region,  it  appears  beyond  doubt  that  the  former  also 
must  have  been  produced  by  deposition  from  fluid  solutions. 

When  we  compare  the  low  solubility  of  certain  ingredients  of  the 
deposits  with  the  spaces  in  which  they  occur,  often  in  large  quantity, 
it  is  impossible  to  assume  that  they  could  have  been  precipitated 
from  solutions  existing  in  these  spaces  only.  We  must  concede  that 
immense  volumes  of  solutions  must  have  flowed  through  the  spaces 
— in  other  words,  that  the  deposits  were  precipitated  from  liquids 
circulating  in  these  channels.  • 

The  formation  of  these  cavities  has  been  already  discussed,  and 
referred  to  mechanical  and  chemical  causes.  It  remains  to  consider 
the  manner  of  their  filling.  We  have  seen  that  the  uppermost  layer 
of  the  ground-water  has  an  apparently  lateral,  but  really  descending 
movement;  and  it  is  very  natural  to  imagine  that  this  top  layer 
slides,  as  it  were,  upon  a  lower  mass,  which  is  apparently  stagnant. 
According  to  this  conception,  the  deep  region  would  be  comparable 
to  a  vessel  filled  with  various  permeable,  impermeable,  and  soluble 
materials,  over  which  water  is  continually  passed,  so  that,  from  the 
moment  when  all  the  interstices  have  been  once  filled,  only  the  upper- 
most water- layer  has  any  movement. 

But,  with  increase  of  depth,  the  pressure  of  the  water-column 
increases,  as  does  the  temperature.  The  warm  water  certainly  tends 
to  rise,  if  not  prevented  by  interstitial  friction,  as  is,  no  doubt,  gen- 
erally the  case.  Bu£  where  the  warmed  water  finds  a  half-opened 
channel  communicating  with  the  upper  region,  it  will  experience 


THE   GENESIS    OF   ORE-DEPOSITS.  25 

much  less  friction  on  the  walls,  and  must  evidently  ascend.  It  might 
thus  be  conceived  that  the  ground-water  descends  by  capillarity 
through  the  rock-interstices  over  large  areas,  in  order  to  mount  again 
through  open  channels  at  a  few  points. 

This  subject  was  viewed  by  A.  Daubre3  in  a  much  wider  signifi- 
cance, and  extended  to  cover  the  origin  of  volcanic  phenomena.*  He 
propounded  the  inquiry,  whether  the  enormous  quantities  of  steam 
which  are  daily  liberated  from  the  deeper  region  are  continually  re- 
placed from  the  surface,  and  if  so,  how?  He  pointed  out  that  this 
water-supply  could  not  take  place  through  open  fissures,  in  which 
the  liquid  water  descended  at  one  time  and  the  steam  ascended  at 
another,  but  he  showed  that  the  descent  could  be  effected  through 
the  porosity  and  capillarity  of  the  rocks.  Jamin's  experiments  have 
taught  us  the  influence  of  capillarity  upon  the  conditions  of  the  equi- 
librium established  by  means  of  a  porous  body  introduced  between 
two  opposing  columns.  Daubree  constructed  an  apparatus  in  which 
the  temperature  in  one  part  of  the  capillary  passage  was  so  high  that 
the  liquid  must  assume  the  form  of  steam,  and  thus  escape  the  op- 
eration of  the  laws  governing  its  infiltration.  This  apparatus  com- 
prised a  sandstone  slab,  with  water  above  and  a  chamber  below,  the 
latter  provided  with  a  manometer  for  measuring  the  pressure  of  the 
steam  collected  in  it.  The  whole  was  exposed  to  a  temperature  of 
about  160°  C.  (320°  F.),  and  steam  collected  in  the  chamber  of  68 
cm.  mercury  column,  indicating  about  13  pounds  over  the  atmospheric 
pressure  in  the  manometer,  or  a  total  pressure  of  about  1.9  atmos- 
phere. This  steam  could  only  come  from  the  water  above  the  sand- 
stone through  which,  in  spite  of  the  pressure,  a  capillary  filtration 
took  place. 

"The  difference  in  pressure  on  the  two  sides  of  the  stone  not  only  did  not  drive 
the  liquid  back,  but  permitted  it  to  filter  quickly  from  the  colder  side  (100°  C.  = 
212°  F.)  to  the  hotter  (160°  C.  =  320°  F.),  and  favored  the  rapid  evaporation  and 
the  drying  of  the  hot  stone  surface"  (op.  cit.,  p.  184). 

"According  to  these  experiments,  therefore,  water  may  be  found  by  capillarity, 
operating  in  the  same  direction  as  gravity,  against  a  strong  interior  counter-pressure 
to  descend  from  the  shallower  and  cooler  regions  to  deeper  and  hotter  ones,  where, 
by  reason  of  acquired  temperature  and  tension,  it  is  capable  of  producing  great 
mechanical  and  chemical  effects"  (op.  dt.t  p.  186). 

Daubree's  experiment  confirms  our  view  that  the  portion  of  the 
ground-water  lying  below  water-level  is  not  stagnant,  but  descends 
by  capillarity,  and  since  it  cannot  be  simply  consumed  in  depth,  re- 

*  Synthetische  Studien  zur  Experimentalgeologie,  by  A.  Daubrde;  German  transla- 
tion, by  Dr.  A.  Gurlt,  Brunswick,  1880,  p.  180. 


26  THE   GENESIS    OF   ORE-DEPOSITS. 

ceives  there  through  a  higher  temperature  a  tendency  to  return 
towards  the  surface,  which  tendency  is  most  easily  satisfied  through 
open  channels.  Stated  summarily:*  The  ground-water  descends  in 
the  deep  regions  also  through  the  capillaries  of  the  rocks;  at  a  cer- 
tain depth  it  probably  moves  laterally  towards  open  conduits,  and, 
reaching  these,  it  ascends  through  them  to  the  surface. 

The  solvent  power  of  the  water  increases  with  temperature  and 
pressure,  and  also  with  the  duration  of  its  underground  journeying. 
Hence,  while  it  is  descending,  it  can  dissolve  or  precipitate  only  the 
more  soluble  substances.  But  the  ascending  current  in  the  open 
conduits  is  undoubtedly  loaded  more  heavily  and  with  less  soluble 
substances,  which,  as  the  conditions  of  their  solubility  (temperature 
and  pressure)  gradually  disappear  in  the  ascent,  must  be  deposited 
in  the  channels  themselves. 

The  open  channels,  in  which  the  solutions  ascend,  are  not  the  de- 
ductions of  theoretical  speculation.  They  really  exist,  as  we  can 
prove  by  induction  from  appropriate  observations. 

The  Ascending  Waters  Encountered  in  Mines. — A  number  of  such 
phenomena  are  adduced  by  H.  Miiller.f  For  instance,  in  the  Gottes 
Geschick  mine,  near  Schwarzenbach,  in  the  Erzgebirge,  at  the  depth 
of  110  m.  (360  feet)  an  acid  spring  containing  CO2and  H2S  emerges 
from  a  nickel-  and  cobaltiferous-silver  ore-vein  (op.  cit.,  p.  286).  At 
the  Wolkenstein  Bad,  an  acid  spring  comes  from  the  druses  of  an 
ore-vein  containing  a  crust  of  barytes  and  amethyst.  In  the  Alte 
Hoffhung  Erbstollen  mine,  near  Mitweida,  bad  air  and  exhalations 
of  carbonic  acid  led,  in  1835,  to  an  analysis  of  the  ground- water, 
which  proved  to  be  weakly  acid.  In  the  Churprinz  mine  at  Frei- 
berg a  warm  (25°  C.  =  77°  F.)  acid  spring  was  struck  on  the  Lud- 
wig  Spat  vein  at  the  depth  of  about  160  m.  (525  feet).  Besides 
these,  Miiller  names  a  number  of  mineral  springs  occurring  in  Bo- 
hemia and  Saxony  at  the  outcrops  of  mineral  veins  never  opened  by 
mining.  In  spite  of  the  great  reserve  which  he  exhibits,  he  sum- 
marizes his  view  as  follows  (op.  cit.,  p.  307)  : 

"Mineral  veins  and  mineral  springs  are  certainly  adapted  to  complement  each 
other  ill  genetic  theory.  On  the  one  hand,  the  ore-veins,  as  extended,  indefinitely 
deep  fissures,  gradually  filled,  indicate  a  very  profound  origin  for  the  mineral 

*  Ueber  die  Bewegungsrichtung  der  unterirdisch  circulirenden  Flilssigkeiten,  von  F. 
Posepny.  Extrait  da  compte  rendu  de  la  3me.  session  du  Congres  geologique  intema- 
tiomd.  Berlin,  1885,  p.  71. 

f  "  Ueber  die  Beziehungen  zwischen  Mineralquellen  und  Erzgangen."  Cotta's 
Gangstudien,  vol.  Hi.,  1860,  p.  261. 


THE   GENESIS   OF   ORE-DEPOSITS,  27 

springs,  and  suggest  variations  caused  by  time  and  circumstances  in  the  amount 
and  mutual  reactions  of  their  contents,  solid  or  volatile;  and,  on  the  other  hand,  (he 
present  relations  of  mineral  springs  explain  the  mode  of  ingress  and  deposit  of  the 
constituents  filling  the  veins." 

Soon  after  this  publication  (I  think  in  1864),  a  thermal  spring  of 
23°  C.  (73°  F.)  was  struck  at  the  depth  of  533  m.  (1774  feet)  in  the 
Einigkeit  shaft,  at  Joachimsthal,  and  in  the  same  mine  at  two  other 
points  similar  mineral  springs,  rising  with  strong  pressure,  were  ex- 
posed. They  prevented  further  increase  in  depth  of  that  part  of  the 
mine,  and  were  plugged  as  far  as  practicable.  The  analyses  made 
in  1882  showed  that  they  were  acid  springs  containing  considerable 
silica  (33  grammes  per  ton.)  In  one  of  them  arsenic  was  also  proved 
to  the  extent  of  22  grammes  per  ton.* 

The  mineral  waters  of  the  Joachismthal  mines  are  said  to  come 
in  contact,  near  the  place  where  they  were  encountered,  with  basalt- 
like  rocks  (called  Wacken),  which  traverse  the  ore-veins,  and  are, 
therefore,  of  later  origin.  In  general,  most  of  the  ore-deposits  of 
the  Erzgebirge  appear  to  have  a  decidedly  recent  origin,  but  even 
from  this  standpoint  the  mineral  springs  found  in  mining  are  to  be 
regarded  as  nothing  else  than  the  continuation  of  those  ascending 
liquids  which  have  filled  the  ore-veins.  Mining  depresses  the  water- 
level,  so  that  mineral  waters  circulating  in  the  neighborhood  are 
forced  to  those  points  in  the  mine  where  there  is  only  atmospheric 
pressure. 

This  "  neighborhood "  may,  indeed,  extend  to  a  comparatively 
long  distance.  For  instance,  the  thermal  spring  at  Carlsbad,  which 
is  the  nearest  to  Joachimsthal,  is  17  kilom.  (10.5  miles)  away  and 
380  m.  (1246  feet)  above  sea-level,  while  the  spring  in  the  Einigkeit 
shaft  at  Joachimsthal  was  struck  at  206  m.  (675  feet  above  sea-level, 
that  is,  174  m.  (571  feet)  lower  than  Carlsbad.  The  irruption  of 
the  thermal  waters  of  Teplitz  in  Bohemia  into  the  lignite-mine  of 
Dux,  7  kilom.  (4  miles)  away,  which  took  place  first  in  1879,  and 
has  occurred  recently  since,  shows  plainly  that  subterranean  com- 
munications may  thus  be  established  for  long  distances  by  raining,  f 

*  Since  the  metric  ton  of  1000  kilo.,  or  the  weight  of  m.3  (1  cubic  meter)  of 
water,  is  a  rational  unit  of  weight,  I  refer  all  tenors  to  it,  and  state  them  in  grammes 
or  milligrammes  to  avoid  decimals.  Thus  22  grammes  per  ton  represents  0.022 
per  thousand,  or  0.0022  per  cent. 

f  "  Einige,  die  Wassereinbriiche  in  die  Duxer  Kohlenbergbaue  betreffende,  geolo- 
gische  Betrachtungen,"  von  F.  Posepny.  Oesterr,  Zcitsch.f.  Berg-u.  Huttenw.t  1888, 
xxx vi.,  pp.  39-54. 


28  {THE   GENESIS   OF   ORE-DEPOSITS. 

Additional  data  for  the  study  of  these  relations  are  furnished  by 
the  miners  on  the  Comstock  lode,  where,  with  the  advancing  depth 
of  operations,  ascending  thermal  waters  were  unexpectedly  encoun- 
tered, the  abundance  and  high  temperature  of  which  presented  extra- 
ordinary obstacles  to  mining.  The  great  richness  of  the  deposit  was 
the  reason  that  the  hope  of  going  deeper  was  not  abandoned,  as  in 
Joachimsthal,  where  the  only  effort  was  to  dam  out  the  waters  from 
existing  workings;  but  that,  on  the  contrary,  the  struggle  was  ac- 
cepted against  the  waters  themselves  and  the  enormous  heat  which 
they  caused  in  the  mines. 

As  is  well  known,  the  upper  workings  on  the  Comstock,  before 
any  ascending  waters  had  been  encountered,  were  not  specially  hot, 
though  warmer  (21°  to  24°  C,  or  70°  to  75°  F.)  than  other  mine- 
workings  in  similar  positions.  Dr.  F.  Baron  v.  Richthofen  noticed 
no  abnormal  mine- temperature,  although  he  ascribed  the  Comstock 
to  earlier  solfataric  action.* 

At  a  later  period,  upon  the  cutting  through  of  clay-partings  in  the 
rock,  the  hot  water  repeatedly  broke  into  the  workings  with  great 
force,  as,  for  instance,  in  the  North  Ophir  mine,  when,  according  to 
Clarence  King,  f  the  workmen  had  scarcely  time  to  escape.  The 
water  is  said  to  have  had  a  temperature  of  40°  C.  (104°  F.),  and 
filled  the  workings  immediately  to  a  height  ot  30  m.  (100  feet).  In 
another  case  the  water  broke  into  the  2200-foot  level  of  the  Savage 
mine,  and  filled  the  large  spaces  both  of  that  mine  and  of  the  Hale 
and  Norcross  up  to  the  1750-foot  level,  or  to  a  height  of  137  m. 
(450  feet).  Gas  was  continually  but  not  violently  evolved  and 
although  Prof.  J.  A.  Church  J  reports  it  to  have  been  under  a  pres- 
sure of  200  pounds  per  square  inch,  he  believes  that  this  was  not  a 
gaseous,  but  a  hydrostatic  pressure. 

The  water  which  in  1880  flooded  the  Gold  Hill  mines  came  from 
a  bore-hole  in  the  Yellow  Jacket  shaft,  at  a  depth  of  939  m.  (:K)80 
feet);  had,  according  to  George  F.  Becker,§  a  temperature  of  77°  C. 
(170°  F.);  and  was  heavily  charged  with  hydrogen  sulphide.  In 
the  upper  levels  of  the  mine,  Becker  says  there  is  evidence  of  the 
presence  of  carbonic  acid,  and  on  the  2700-foot  level  where  the  tera- 

*  The  Comstock  Lode,  Its  Character  and  Probable  Mode  of  Continuance  in  Depth, 
San  Francisco,  1866,  p.  54. 

t  U.  S.  Geol.  Expl.  of  the  40th  Parallel,  vol.  iii.  Mining  Industry,  Washington, 
1870,  p.  87. 

I  The  Comstock  Lode,  Its  Formation  and  History,  New  York,  1879,  p.  207. 

I  "  Geology  of  the  Cotnstock  Lode,"  etc.,  U.  S.  Geol.  Suwey,  Washington,  1882, 
pp.  230,  386. 


THE   GENESIS   OF   ORE-DEPOSITS.  29 

perature  was  66°  C.  (150°  F.)  a  deposit  of  sinter  was  found,  con- 
sisting mainly  of  carbonates.  Church  (p.  206)  remarks,  that  it  was 
at  first  believed  that  the  repeated  irruptions  of  water  came  from 
chains  of  cavities  existing  in  the  rock,  but  that  at  the  time  of  his 
visit  the  conviction  was  that  they  came  through  shattered  and  de- 
composed seams,  parallel  with  the  lode,  and  sometimes  of  great 
thickness. 

Systematic  and  long-continued  temperature-observations  in  several 
Oomstock  mines  enabled  Becker  to  represent  comprehensively  for 
different  lines  the  increase  of  temperature  with  depth;  and  it  thus 
appeared  that  this  increase  was  greatest  in  the  vicinity  of  the  lode, 
diminishing  with  the  distance  from  the  lode;  that  the  vehicle  of 
heat  was  the  water ;  and  hence  that  it  was  through  the  lode  itself 
that  communication  with  the  hot  depths  took  place,  and  the  phe- 
nomenon denominated  "  solfataric  action  "  by  Kichthofen  was  caused. 

The  chemical  constitution  of  these  intruding  waters  will  be  con- 
sidered further  on,  after  certain  phenomena  occurring  nearer  to  the 
surface  have  received  attention. 

Related  Phenomena  Near  the  Surface. — A  sort  of  transition  to  the 
corresponding  phenomena  on  the  surface  itself  is  illustrated  by  the 
mines  at  Sulphur  Bank,  Cal.,  which  have  furnished  some  of  the 
most  important  data  contributed  by  America  to  the  study  of  the 
genesis  of  ore-deposits. 

This  is  a  once  rich,  but  now  (apparently)  practically  exhausted 
quicksilver-mine,  in  the  working  of  which  not  only  thermal  waters 
but  gaseous  emanations  were  encountered  as  obstacles.  At  the  time 
of  my  visit  in  1876,  an  open-cut  exploitation  was  in  progress,  the 
terraces  of  which  had  extended  in  some  places  about  5  m.  (16  feet) 
below  the  natural  surface.  Sulphur,  as  well  as  quicksilver,  was  won ; 
but  it  subsequently  appeared  that  the  sulphur-deposit  was  confined 
to  the  uppermost  zone,  while  the  quicksilver  (or  cinnabar)  extended 
in  considerable  proportions  to  deeper  regions. 

At  that  time  I  found  sulphur  and  cinnabar  in  a  decomposed 
basalt,  partly  as  the  filling  of  irregular  fissures,  traversing  the  rock 
in  all  directions,  partly  as  impregnations  in  the  rock  itself,  which 
had  often  been  reduced  to  a  porous  mass.  The  process  of  decom- 
position proceeded  unquestionably  from  the  fissures,  which,  more- 
over, gave  forth  hot  mineral  waters  and  gases.  The  odor  alone  was 
sufficient  proof  that  the  gases  contained  H2S,  to  the  oxidation  of 
which  into  SH2O4the  acid  reaction  of  the  rock  and  its  moisture  was 
to  be  ascribed.  The  miners  (mostly  Chinese)  chiefly  followed  in 


30  THE   GENESIS   OF   ORE-DEPOSITS. 

extraction  the  fissures  (partly  because  it  was  the  easiest  way  to  make 
rapid  progress ;  partly  because  the  richest  ores  were  there  concen- 
trated) ;  and,  as  a  result,  large  round  blocks,  often  several  meters  in 
diameter,  were  left  standing.  These  had  a  distinct  shaly  structure, 
but  were  so  loosely  held  together  that  a  kick  would  reduce  them  to 
ruins.  In  the  interior  of  the  larger,  light-gray  blocks,  was  often 
found  a  nucleus  of  solid,  dark,  undecomposed  rock.  (Some  of  these 
nuclei  I  have  added  to  the  collection  of  the  Przibram  Mining 
Academy.) 

The  cracks  were  filled  chiefly  with  an  opaline  mass,  in  which  a 
white,  opaque  ingredient  was  variously  kneaded,  as  it  were,  with  a 
gray  to  black  one,  translucent  at  the  edges.  The  specimens  taken 
fell  into  irregular  pieces,  bounded  by  fissures,  evidently  the  result 
of  loss  of  volume  or  loss  of  moisture  by  the  opaline  mass. 

The  cinnabar  formed  either  distinct  mineral  crusts  in  the  crev- 
ices or  impregnations  of  the  porous  neighboring  rock.  This  was 
true  of  the  sulphur  also;  only,  the  latter  appeared,  as  a  rule,  in 
crystalline  aggregates  upon  the  cinnabar  crusts — an  indication  of  its 
later  origin.  Occasionally  the  cinnabar  was  deposited  in  beautiful 
crystals  on  the  fissure-walls,  but  these  were  generally  so  loosely  at- 
tached that  it  was  difficult  to  secure  a  specimen. 

The  pyrites,  mostly  disseminated  in  the  rock,  tended  so  strongly  to 
decomposition,  evidently  by  reason  of  its  saturation  with  sulphuric 
acid,  that  specimens  containing  it  soon  fell  to  pieces. 

These  observations  suffice  to  show  that  in  this  case  hot  mineral 
waters  ascend  through  fissures  containing  ore-crusts  and  opaline  de- 
posits; and  when  it  is  considered  that  the  deposit  of  amorphous,  hy- 
drated  silica  is  unquestionably  the  work  of  the  mineral  water  which 
decomposed  the  rock,  and  also,  that  the  cinnabar  occurs  in  the  in- 
terior of  the  opaline  mass,  the  two  phenomena  cannot  well  be  sepa- 
rated, and  it  must  be  assumed  that  a  metallic  sulphide  has  here  been 
deposited  from  an  ascending  spring.  Fig.  10  represents  the  exposure 
as  sketched  in  ray  note-book. 

Later  developments  exhibit  these  relations  still  more  clearly.  Le 
Conte  and  Becker*  found  a  shaft  50  m.  (164  feet)  from  the  basalt, 

*  "The  Phenomena  of  Metalliferous  Vein-Formation,  Now  in  Progress  at  Sul- 
phur Bank,"  by  J.  Le  Conte  and  YV.  B  Rising,  Am.  Jour,  of  -Set.,  xxv.,  p.  424. 

"On  Mineral  Veins,  Now  in  Progress  at  Steamboat  Springs,  Compared  with  the 
same  at  Sulphur  Bank,"  by  J.  Le  Conte,  Am  Jour,  of  Sci.  xxv.  p.  424. 

"Geology  of  the  Quicksilver- Deposits  of  the  Pacific  Slope,"  by  G.  F.  Becker, 
Monograph  U.  S.  Geol.  Surv.,  Washington,  1888,  p.  251. 


THE   GENESIS   OF   ORE-DEPOSITS.  31 

about  92  m.  (310  feet)  deep  in  sandstone,  from  which  drifts  had 
been  run  northward  at  different  levels  under  the  outcrops  of  the  de- 
posit. It  is  to  be  regretted  that  their  reports  are  not  accompanied 
with  precise  descriptions  of  the  mine-workings.  In  the  third  level 
(64  m.  =  210  feet  below  the  surface)  the  drift  was  70  m.  (232  feet) 
long,  "cutting  th rough  the  ore-body  and  reaching  only  barren  rock  on 
the  other  side.  The  fourth  level  has  been  pushed  31  m.  (136  feet), 
and  has  reached  the  ore-body."  From  these  data  it  is  hardly  pos- 
sible to  form  an  idea  of  the  position  of  the  ore- body  traversed. 

The  data  given  concerning  the  interior  structure  of  the  deposits 
are,  however,  important.  Sandstones  and  slates  are  here  broken  up 
by  fissures  in  suc-h  a  way  as  often  to  form  a  breccia.  Whether  the 
fragments  belong  together,  and  whether  they  present  the  relation 
which  I  have  denominated  typhonic,  is  not  stated;  but  it  may  be  in- 
ferred from  the  sketch  of  an  ore-specimen  from  this  place  that  the 
fragments  do  not  belong  together,  and  that  their  condition  has  been 
brought  about  by  more  extreme  dislocations.  The  subject  is  highly 
important  for  us;  and  I  have  attempted  in  Fig.  11,  although  the 
original  is  not  before  me,  to  represent  it  according  to  Le  Oonte's 
sketch,  so  as  to  place  it  side  by  side  with  other  phenomena,  thor- 
oughly familiar  to  me. 

The  fragments  of  slate  and  sandstone  have  somewhat  rounded 
edges,  and  leave  varied  interspaces,  which  are  filled,  partly  with  a 
still  soft  or  already  indurated  paste,  containing  finely  disseminated 
metallic  sulphides,  partly  with  cinnabar,  for  the  most  part  in  co- 
herent crusts.  A  part  of  the  space  is  usually  empty,  exhibiting  what 
I  call  a  central  druse.  Sometimes,  it  is  said,  the  rock-  fragments  are 
cemented  together  with  massive  cinnabar,  and  kernels  of  rock  crusted 
with  cinnabar  occur  frequently. 

Hot  mineral  water  and  gases  carrying  H2S  force  their  way  through 
the  interstices  of  the  deposit,  as  was  the  case  observed  in  the  upper 
zones.  The  silica  deposits  are  found  in  all  stages  of  consolidation, 
from  a  gelatinous  mass  to  chalcedony  and  (Le  Conte,  op.  cit.,  p.  29) 
alternate  with  layers  (crusts)  of  metallic  sulphides  (cinnabar  and 
pyrites).  Becker  examined  the  whole  neighborhood,  and  extended 
his  studies  to  similar  ore-deposits  of  the  region.  He  does  not  con- 
sider the  basalt  of  Sulphur  Bank,  as  do  G.  Holland,*  and  Le  Conte, 
to  be  a  lava-stream,  but  takes  it  to  be  an  eruptive  rock,  originating 
on  the  spot,  which  has  overflowed  a  fresh- water  formation  of  recent 

*  '  Les  Giseraonts  de  Mercure  de  Californie,"  Annales  des Mines,  1878,  p.  26. 


32  THE   GENESIS   OF   ORE-DEPOSITS. 

age.  The  bottom  proper  is  a  Cretaceous  sandstone.  The  ore-bear- 
ing character  extends  from  the  basal  t(  about  16m.  =  52  feet  thick) 
through  the  fresh -water  layers  in  to  the  Cretaceous  sandstone.  Concern- 
ing its  relations  in  the  middle  layer  we  have  no  data,  which  is  unfor- 
tunate, since  the  effects  of  the  acid  waters  upon  this  calcareous  material 
must  have  been  considerable,  and  it  is  not  unlikely  that  the  deposit 
had  in  this  region  a  totally  different  character.  Fresh-water  forma- 
tions adjoining  the  deposit  have  preserved  to  a  remarkable  degree 
plant-roots  etc.,  transformed  into  lime  carbonate;  and  it  would  be 
very  instructive  to  study  their  forms  as  metamorphosed  by  the  min- 
eral water. 

Concerning  the  chemical  constitution  of  the  warm  (80°  C.  = 
176°  F.)  water,  I  shall  speak  further.  According  to  Becker's  anal- 
ysis (op.  cit.,  p.  *^59),  it  is  extraordinarily  rich  in  chlorides,  borax  and 
sodium  carbonate.  The  gas  liberated  from  it  often  proved  to  be 
ammoniacal,  and  consisted  in  1000  parts  of  893  parts  CO2,  2  parts 
H2S,  79  parts  CH4  (marsh-gas)  and  25  parts  nitrogen. 

As  to  the  presence  of  other  metals  besides  mercury,  it  is  worthy 
of  mention  that  Dr.  Melville  found  small  amounts  of  gold  and 
copper  in  the  marcasite  accompanying  the  cinnabar,  and  that  G. 
Becker  found  in  the  efflorescence  from  the  mine-workings,  besides 
the  substances  detected  in  the  mineral  water,  traces  of  cobalt  and 
nickel. 

As  will  be  seen,  this  deposit  furnishes  genetic  data,  concerning  not 
only  the  ores  of  quicksilver,  but  also  those  of  other  metals.  An  as- 
cending mineral  spring  here  passes  from  the  deep  into  the  shallow 
region,  and  suffers,  besides  the  reduction  of  pressure  and  tempera- 
ture, the  oxidation  of  its  H2S,  from  which  result  a  strong  acid  and 
the  deposition  of  sulphur  nearest  the  surface. 

In  depth  no  sulphur  is  found,  but  sulphides  of  quicksilver  and 
iron,  upon  or  within  deposits  of  silica,  both  being  in  distinct  alter- 
nating mineral  crusts.  It  cannot  be  doubted  that  cinnabar  and  py- 
rites, on  the  one  hand,  and  silica,  on  the  other,  have  been  precipi- 
tated from  the  solution  which  still  ascends  in  these  channels.  At 
most,  it  may  be  doubted  whether  this  precipitation  is  still  going  on. 
Le  Conte  adduces  in  support  of  the  probable  continuance  of  the 
process  the  occurrence  of  silica  sometimes  gelatinous  and  soft,  as  if 
recently  precipitated.  Becker  and  Melville  tried  to  obtain  direct 
evidence  of  the  presence  of  quicksilver  dissolved  in  the  ascending 
mineral  water  of  to-day,  but  their  careful  investigations  failed  to 
find  it.  Although  the  water  contains  ingredients  in  which  quick- 


THE   GENESIS   OF   ORE-DEPOSITS.  33 

silver  is  soluble,  there  is  no  quicksilver  dissolved,  and  it  must  have 
been  already  precipitated  by  some  agent — as  they  suggest,  ammonia. 

There  are  among  geologists  unbelieving  Thomases  enough,  who 
will  believe  in  the  presence  of  quicksilver  in  the  mineral  solution 
only  when  it  has  been  actually  precipitated  for  them;  but  there  are 
those,  on  the  other  hand,  who  are  convinced  by  the  evidence  thus 
far  gathered  that  the  sulphide  deposits  of  this  locality  proceeded  from 
the  ascending  thermal  spring,  whether  the  process  of  precipitation 
is  still  going  on  or  not. 

Equally  weighty  data  are  furnished  by  Steamboat  Springs  in  Ne- 
vada, to  which  Laur  and  J.  A.  Phillips  first  called  attention,  and 
which  Le  Conte  and  Becker  investigated  thoroughly.*  In  a  valley 
surrounded  with  eruptive  rocks,  but  underlain  chiefly  by  Archaean 
rocks,  thermal  springs  may  be  seen  at  several  points  emerging  from 
north-and-south  fissures.  The  action  of  these  springs  has  covered 
the  ground  with  a  sinter-deposit,  predominately  of  lime  carbonates, 
about  15  ID.  (49  feet)  thick.  In  this  sinter  may  be  traced  many  fis- 
sures, here  and  there  still  open,  but  mostly  closed  by  the  deposit  of 
silica  on  their  walls.  According  to  a  sketch  given  by  Le  Conte, 
these  very  clearly  crustified  deposits  extend  somewhat  above  the 
general  level  of  the  surface,  forming  single  mounds  or  chains  of 
mounds. 

From  some  of  them  hot  vapors  and  gases  still  issue,  chiefly  C02 
containing  H2S.  In  others,  such  emanations  have  been  so  greatly 
diminished  that  only  by  listening  can  the  liberation  of  vapor  in 
depth  be  perceived.  Some  of  the  fissures  are  completely  filled,  and 
give  forth  neither  mineral  water,  steam  nor  gas. 

In  the  group,  about  200  m.  (656  feet)  wide  and  1  kilom.  (0.6 
mile)  long,  which  lies  nearest  to  the  rail  way- track,  these  phenomena 
are  most  strikingly  exhibited.  Besides  the  principal  substances 
mentioned  below  in  the  table,  Becker  found  in  this  mineral  water 
also  small  amounts  of  metallic  compounds,  as,  for  instance,  HgS,  a 
trace  of  Na2S,  1.0  gramme  per  ton  of  Na2SbS3,  and  8.7  grammes  per 
ton  of  Na2AsS3. 

*  M.  Lnur,  "  Sur  le  gisement  et  Pexploitation  de  Tor  en  California,"  Annales  dcs 
Mines,  1863,  iii.,  p.  423. 

J.  A.  Phillips,  Phil.  Mag.,  1871,  xlii.,  p.  401.     Also,  A  Treatise  on   Ore-Deposits, 
London,  1884,  p.  70. 

J.  Le  Conte,  "  On  Mineral  Veins  now  in  Progress  at  Steamboat  Springs  Com- 
pared with  the  Same  at  Sulphur  Bank,"  Am.  Jour.  Sci.,  xxv.,  p.  424. 

G.  F.  Becker,  "Geology  of  the  Quicksilver-Deposits  of  the  Pacific  Slope,"  Mono- 
graph U.  S.  Geol  Survey,  Washington,  1888,  p.  331. 

3 


34  THE   GENESIS   OF   ORE-DEPOSITS. 

About  1J  kilom.  (1  mile)  to  the  west  is  a  group  of  similar  fissures^ 
yielding  some  steam  and  CO2,  but  no  mineral  water.  In  the  min- 
eral crusts  of  these,  however,  several  metallic  sulphides  occur.  In 
1863,  Laur  declared  that  he  had  seen  in  them  distinct  traces  of 
gold.  In  1878,  one  of  these  fissures  was  opened  by  an  adit,  about 
15m.  (49  feet)  under  the  surface,  and  produced  a  vein-matter  carry- 
ing cinnabar,  which  was  mined  for  a  while  as  quicksilver-ore.  The 
temperature  of  this  mine  was  not  so  high  as  to  cause  serious  trouble 
to  the  workmen. 

G.  F.  Becker  carefully  analyzed  the  filling  of  several  fissures,  and 
found,  besides  hydrated  ferric  oxide,  considerable  quantities  of  Sb, 
As,  Pb,  Cu,  Hg  sulphides  and  gold  and  silver,  as  well  as  traces  of 
Zn,  Mn,Coand  Ni.  Since  from  1  to  3.5  kilog.  (2.2  to  7.7  lbs.)of  the 
vein-stuff  were  employed  for  each  analysis,  the  results  are  specially 
trustworthy,  and  I  give  the  records  of  three  analyses  here,  express- 
ing them  in  grammes  per  ton  (1  ton  =  1,000,000  grammes) : 

i.  n.  in. 

Sulphides  of  antimony  and  arsenic,     23,000.0  150.0 

Ferric  oxide,        2,500.0         

Sulphide  of  mercury, 1.4  2.5  10 

Lead, 88.0  21.0 

Copper,         .        .        .        .  '     .        .       ..03  12.0         

Gold,   .        .        ,        .        .        .  *'    .        .09  1.0 

Silver, 0.3  0.3         

(Considering  the  gold  and  silver  to  be  alloyed  in  the  above  pro- 
portions, we  should  have  bullion  0.750  and  0.769  fine,  which  is  the 
general  grade  of  the  so-called  "  free  gold  "  of  Transylvania.) 

The  careful  study  of  the  phenomena,  particularly  by  G.  F.  Becker, 
leaves  no  doubt  that  in  this  case  ascending  mineral  waters  have  de- 
posited, besides  the  various  forms  of  silica  (from  opal  to  crystalline 
quartz),  different  metallic  sulphides,  and  that  the  fissure-fillings  ex- 
hibit a  very  clear  instance  of  crustification.  It  is,  indeed,  not 
proved  that  the  process  is  now  going  on.  But  that  is  not  the  main 
point.  We  may  be  content  to  have  the  proof  that  it  has  taken  place. 

Mineral  Springs  at  the  Surface. — When  we  isolate  a  spring  char- 
acterized by  high  temperature,  a  large  quantity  of  gas  or  of  matter 
in  solution,  we  notice  at  once  that  its  level  is  higher  than  that  of 
the  ground-water.  The  more  thorough  the  isolation  or  walling-in, 
the  more  striking  is  this  phenomenon,  so  clearly  unlike  that  of  the 
vadose  or  shallow  circulation. 

Isolation  is  usually  performed  by  digging  as  deep  as  possible,  so 


THE   GENESIS   OF   OEE-DEPOSITS.  35 

as  to  get  at  the  spring  below  the  loose  surface-material  in  an  imper- 
meable rock,  and  then  by  building  a  well-pit,  to  give  it  freer  ascent. 
But  since  the  circulation  of  the  ground- water  in  the  loose  surface  is 
very  lively,  the  necessary  depression  of  the  water-level  in  such  an 
excavation  involves  the  lifting  of  large  quantities  of  water.  More- 
over, the  escape  of  gas  from  the  mineral  spring  often  hinders  the 
operation  ;  so  that  there  is,  as  a  rule,  little  opportunity  for  thorough 
investigations.  Cases  in  which  accurate  observations  have  been 
properly  recorded  for  preservation  are  very  rare. 

The  first  good  fissure  encountered  in  the  bed-rock  is  deemed  to  be 
the  channel  of  the  mineral  spring,  and  the  well  is  built  over  it. 
Complete  isolation  from  the  ground-water  is  probably  seldom 
practicable.  Nevertheless,  the  mineral  spring,  being  under  higher 
pressure  than  the  ground-water,  will  tend  to  exclude  it  from  the 
well.  The  imperfection  of  the  isolation  is  shown,  however,  when 
we  try  for  any  reason  to  pump  out  the  well.  To  lower  the  water- 
level,  say  1  m.  (3.28  feet),  we  have  to  raise  many  times  the  amount 
of  water  which  the  spring  itself  would  normally  furnish  (even  taking 
into  account  the  decreased  pressure,  which  affects  the  flow  in  the 
proportion  of  the  square  root  of  the  head).  The  excess,  generally 
surprisingly  great,  comes  from  the  ground-water  which  finds  its  way 
into  the  well. 

If  we  allow  the  mineral  water  to  ascend  again  quietly  in  the  well, 
the  level  rises  at  first  rapidly,  then  slowly,  and  finally  remains  (in 
the  absence  of  change  in  the  height  of  the  ground -water  and  in  the 
barometric  pressure)  stationary  at  a  certain  height  above  the  ground- 
water  level.  This  difference  of  height  represents  the  ascensional 
force  of  the  mineral  spring. 

If  the  spring  makes  a  deposit  at  its  mouth  (mostly  of  lime  car- 
bonate, hydrated  ferric  oxide,  and  silica)  it  may  thus  build  a  con- 
duit, extending  above  the  ground-water  level  and  the  surface  to  the 
height  represented  by  its  ascensional  force.  Thus,  we  find  conical 
mounds  from  the  top  of  which  mineral  springs  flow.  This  phenom- 
enon is  shown  in  the  highest  degree  by  geysers,  i.e.,  thermal  springs 
in  which  paroxysmal  developments  of  steam  and  gas  occur,  often 
forcing  the  water  to  notable  heights.  Some  of  the  magnificent  gey- 
sers of  the  Yellowstone  National  Park  have  built  chimney-like  con- 
duits of  considerable  size.  Their  structure  has  much  similarity  to 
that  of  stalactites ;  indeed,  we  may  recognize  generally,  in  the  various 
deposits  of  ascending  mineral  springs  (in  other  words,  in  the  prod- 
ucts of  the  deep  circulation),  many  analogies  with  the  vadose  circu- 


36  THE   GENESIS   OF   ORE-DEPOSITS. 

lation.  This  circumstance  indicates  a  relation  between  the  phenom- 
ena of  the  two  regions  which  is  often  entirely  ignored  or  even  de- 
nied. 

While,  for  instance,  the  geysers  have  a  temperature  above  boiling- 
point,  some  mineral  springs  rise  but  little  above  the  mean  local  tem- 
perature of  the  surface  or  of  the  ground-water.  This  may  be  es- 
pecially observed  in  the  acid  springs  ;  yet,  these  are  also  ascending 
springs,  and  must  have  been  formed  in  the  deep  region. 

Within  the  vadose  region  we  have,  sometimes,  ascending  waters, 
which  are,  however,  mostly  to  be  explained  by  hydrostatic  pressure. 
But,  within  the  deep  region,  hydrostatic  pressure  can  play  no 
part ;  and  here  it  is  the  higher  temperature  and  the  presence  of 
gas  which  cause  the  ascension  of  mineral  springs.  The  extreme 
instances  of  this  kind,  such  as  geysers,  steaming  springs,  mud-vol- 
canoes, petroleum  springs,  etc.,  nobody  will  undertake  to  explain  by 
hydrostatic  pressure,  and  more  moderate  results  of  the  same  factors 
can  scarcely,  with  consistency,  be  so  explained. 

It  is  a  striking  circumstance  that  ascending  springs  occur  chiefly 
in  the  neighborhood  of  the  later  eruptive  rocks,  such  as  trachyte, 
basalt,  etc.  This  is  emphatically  the  case  throughout  the  zone  which 
crosses  Europe  from  west  to  east,  in  France,  Germany,  Bohemia, 
Hungary,  and  Transylvania.  Here  the  warm  springs  and  the  acid 
springs  occur  thickly,  while  north  and  south  of  this  zone  they  are 
only  sporadic.  Their  connection  in  the  zone  with  the  eruptive  rocks 
is  evident,  and  they  are  often  considered  as  the  last  echoes  of  the 
processes  of  eruption.  The  sporadic  springs,  in  places  where  erup- 
tive rocks  play  no  part,  must  have  come  through  deep  fissures  of 
dislocation.  For  example,  the  line  of  the  fault  along  which  the  Alps 
sank  below  the  Tertiary  basin  of  Vienna  is  marked  by  a  complete 
series  of  thermal  springs. 

This  circumstance  has  another  and  far-reaching  significance.  For 
ore-deposits  are  similarly  distributed.  They  are  most  numerous  and 
most  closely  grouped  in  the  neighborhood  of  eruptive  rocks,  espec- 
ially extended  zones  of  eruptive  rocks,  as  in  the  American  West,  and 
in  Hungary  and  Transylvania,  while  among  other  rocks  they  are 
fewer  and  more  scattered. 

Chemical  Constitution  of  Mineral  Waters. — Ascending  mineral 
springs  have  widely  varying  composition ;  some,  like  the  "  aeroth- 
erms,"  representing  strictly  only  warmed  ground-water,  while  others 
are  strongly  mineralized,  and  carry  some  substances  almost  to  sat- 
uration. The  material  bearing  on  this  subject  is  too  voluminous 


THE   GENESIS   OF   OKE-DEPOSITS. 


37 


and  heterogeneous  to  be  fully  cited  and  discussed  here.  I  must  be 
content  with  the  exhibit  of  a  few  analyses,  specially  interesting  for 
the  present  purpose. 

The  following  is  a  list  of  the  localities,  etc.,  represented  in  the 
table  below : 


Waters  Encountered  in  Mines. 

No.                        Locality.                                               Temperature.  Authority. 

1  Gottesgeschick  mine,  Schwarzenberg,          .     11.      38.1  R.  Kichter. 

2  Einigkeits  shaft,  Joachimsthal,    .         .         .     28.7   47.9  J.  Seifert. 

3  The  "  Sprudel,"  in  Colliery  at  Briix,  Bohemia,  J.  Gintl. 

4  Comstoek,  Savage,  600  feet  level,          .         .     28.  ?  47.6  ?  S.  W.  Johnson. 

5  Comstoek,  Gould  and  Curry,  1700  feet  level,      48.  ?  58.6  ?  S.  W.  Johnson. 

6  Comstoek,  Gould  and  Curry,  1800  feet  level,      50.  ?  59.8  ?  S.  W.  Johnson. 

7  Comstoek,  Hale  and  Norcross,     .        .        .     70.  ?  70.9  ?  S.  W.  Johnson. 

8  Comstoek,  Ophir, 40.  ?  52.2  ?  Attwood. 


No. 


Water  in  Ore-bearing  Fissures. 

Locality.  Temperature.  Authority. 


9  Sulphur  Bank,  Herman  shaft, 

10  Sulphur  Bank,  Parrot,  shaft, 

11  Steamboat  Springs, 


70.  ?  70.9  ? 
70.     70.9 
75.     73.7 


No. 


Some  Bohemian  Thermal  Springs. 

Locality.  Temperature. ' 


12  Sprudel,  Carlsbad, 

13  Kreuzbrunn,  Marienbad, 

14  Wiesenquelle,  Franzensbad, 

15  Urquelle,  Teplitz, 


64.  67.6 

12.  38.7 

13.  39.2 
50.  59.8 


Weak  and  Strong  Mineral  Springs. 


No.  Locality. 

16  Ottoquelle,  Giesshiibel, Dr, 

17  Josephsquelle,  Bilin  (1875), 

18  Puita  de  P  Enclos  des  Celestins,  Vichy, 

19  Kippoldsau,  Josephsquelle  (1875),     .        .        . 

20  Kippoldsau,  Wenzelquelle  (1875),      .... 

21  Kippoldsau,  Leopoldquelle  (1875),     .... 

22  Kissingen,  Pandurquelle  (1856),         .... 

23  Kissingen,  Kakoczyquelle  (1856),        .... 

24  Yellowstone,  Cleopatra,  Mammoth  Hot  Springs  (1888),  \ 

25  Yellowstone,  Grand  Geyser, / 


G.  F.  Becker. 
G.  F.  Becker. 
G.  F.  Becker. 


Authority. 

Novak  Kratschmann. 

Dr.  Kuppert. 

Bunsen. 

Bunsen. 

Bunsen. 

Bunsen. 

Liebig. 

Liebig. 

F.  H.  Gooch, 

T.E.  Whitefield. 


It  is  well  known  that  analysts  in  combining  their  results  do  not 
follow  the  same  rule.     One  supposes  a  certain  acid  to  be  united  with 


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THE   GENESIS   OF   ORE-DEPOSITS.  39 

an  alkali;  another  gives  the  same  acid  to  an  earthy  base,  etc.  What 
interests  us  in  the  comparison  afforded  by  the  table  is  the  substances 
occurring  in  large  proportions,  the  carbonates  and  sulphates  of  the 
alkalies  and  alkaline  earths ;  the  chlorides,  the  silica,  and  the  quan- 
tity of  organic  matter  (if  it  were  determined  by  a  uniform  proce- 
dure). 

I  deem  it  most  convenient  to  take  1  ton  of  1000  kilogrammes 
(representing,  for  waters  not  too  rich  in  mineral,  the  weight  of  1  cubic 
meter),  and  to  express  the  weights  of  the  salts  in  grammes,  to  avoid 
decimals.  In  order  to  show  the  relations  of  the  salts,  one  to  another, 
it  is  well  also  to  represent  them  on  the  basis  of  1000  parts  of  the 
solid  matter. 

For  the  Comstock  waters,  the  rationally-stated  analysis  of  S.  W. 
Johnson,  from  the  600  faot  level  of  the  Savage  mine  (C.  King,  op. 
cit.j  p.  87),  served  me  as  a  guide,  according  to  which  I  have  recalcu- 
lated the  figures  (Church,  op.  cit.,  p.  204),  for  other  mines  and  levels. 

These  analyses  show  the  irruptive  waters  on  the  Comstock  to  be 
poor  in  dissolved  substances.  According  to  the  determination  of 
solid  residuum  by  E.  S.  Bristol  (C.  King,  I.  c.,  p.  88),  this  would  not 
be  the  case.  He  finds  the  mine-water  of  the  500  feet  level  to  con- 
tain in  the  Savage  north  drift  2660  grammes,  and  in  the  Yellow 
Jacket  west  drift  as  much  as  3271  grammes  of  solid  material  in  one 
ton  (1000  kilos.).  But  it  is  a  question  whether  these  figures  do  not 
refer  to  ordinary  mine-waters,  as  the  term  west  drift  seems  to  indi- 
cate. 

The  predominance  of  sulphates  over  carbonates  is  nothing  un- 
usual ;  but  the  decided  predominance  of  lime,  sulphate  or  gypsum 
in  the  Comstock  waters  is  unique.  This  relation  would  still  remain 
if  we  should  reckon  a  part  of  the  sulphuric  acid  as  combined  with 
the  alkalies.  The  two  most  trustworthy  analyses  of  Attwood  and 
Johnson  give  222  and  535  grammes  of  gypsum  per  ton  of  water,  and 
492  and  700  grammes  per  ton  of  dry  residuum.  Apart  from  their 
gypsum,  the  Comstock  irruptive  waters  may  be  classed  among  the 
weak  or  acrothermal  springs,  like  those  of  Teplitz  in  Bohemia. 

The  Sulphur  Bank  and  Steamboat.  Springs  waters  are  distinguished 
from  all  others  in  the  table  by  a  considerable  proportion  of  sodium 
biborate,  and  resemble  unmistakably  certain  Suffioni  and  Lagoni 
waters  of  Middle  Italy.  Their  degree  of  impregnation  and  their 
large  proportion  of  chlorides  bring  them  near  the  waters  of  Carls- 
bad and  Franzensbad,  Bohemia.  The  proportion  of  sodium  chloride 
is  not  surprising  in  the  American  West,  in  the  neighborhood  of  un- 


40  THE   GENESIS    OF   ORE-DEPOSITS. 

drained  and  therefore  salt  regions,  but  it  is  surprising  in  Bohemia,  a 
country  notoriously  free  from  salt,  in  which  no  rock  is  known  to  con- 
tain these  highly  soluble  substances.  We  must  assume  that  they 
exist  in  the  deeper  region,  in  forms  not  yet  decomposed,  such  as  soda- 
lite  (3Na2Al2Si2O8  +  2NaCl)  which  must  be  chemically  decom- 
posed before  its  NaCl  can  be  dissolved.  The  presence  of  quantities 
of  salt  smaller  than  those  here  under  consideration  can  be  attributed 
(as  I  at  one  time  attempted  to  show*)  to  atmospheric  precipitation. 
A.  Bobierref  found  by  careful  and  continuous  analysis  of  the  rain- 
water falling  in  Nancy  throughout  the  year  1863,  14  grammes 
of  salt  per  ton  or  cubic  meter ;  and  G.  ZoppeJ  has  argued  that  the 
sometimes  considerable  contents  of  sodium  chloride  in  the  springs  of 
the  Iglesiente  district,  in  the  island  of  Sardinia,  can  only  be  explained 
by  the  transportation  of  salt  from  the  sea  by  wind.  (A  stormy 
cloud-burst,  March  7,  1886,  showed  as  much  as  387  grammes  per 
ton  or  cubic  meter).  The  salt  of  the  atmospheric  precipitation  is 
concentrated  by  evaporation.  In  Bohemia,  for  instance,  only  one- 
fourth  of  the  rainfall  escapes  into  the  Elbe ;  in  more  southern  regions 
the  whole  evaporates.  The  descending  ground- water  is  still  further 
concentrated ;  so  that  in  this  way  the  salt  normally  found  in  the 
-ascending  waters  may  be  accounted  for. 

But  while  the  water  of  Steamboat  Springs  is  rich  in  sodium  chlo- 
ride, the  Comstock  mine-water  is  poor,  notwithstanding  the  compara- 
tively near  neighborhood  of  the  two  places.  Both  adjoin  eruptive 
rocks,  especially  basaltic  outflows;  but  the  Steamboat  Springs  break 
out  of  crystalline  rocks.  May  not  the  ascending  waters  have  derived 
their  abundant  sodium  chloride  from  minerals,  like  sodalite,  which 
contain  it  chemically  bound  ? 

Hydrogen  sulphide  plays  an  important  part  in  the  ascending 
waters.  Its  presence  seems  to  be  the  cause  of  a  greater  abundance 
of  dissolved  substances.  It  is  attributed  to  the  decomposition  of 
sulphates  through  the  organic  matter,  traces  of  which  are  found  in 
most  of  the  ascending  waters.  By  re-oxidation,  it  produces  the  sul- 
phuric acid  which  transforms  carbonates  into  sulphates.  It  is  re- 
markable that  in  many  mineral  springs  H2S  appears  periodically  in 
surprising  excess,  and  often  disappears  again,  almost  without  leaving 

*  "  Zur  Genesis  der  Salzablagerungen,  besonders  jener  im  nordam.  Westen,"  k.  k. 
Akadd.  Wissemch.,  Wein,  1877. 

f  Compt.  rend.,  Iviii ,  p.  755.     Bullet.  Soc.  Chim.,  liv.,  p.  467. 

J  "  Descrizione  geologico-mineraria  dell'  Iglesiente,"  Memorie  descritt.  deUa  Carta 
gert.  d' Italia,  iv ,  Rojaa,  1333,  p.  119. 


THE   GENESIS   OF    OEE-DEPOSITS.  41 

a  trace.  It  is  probable  that  an  alternation  of  the  processes  of  oxida- 
tion and  reduction  would  produce  this  phenomenon. 

The  most  important  geological  factor  in  ascending  waters  is  un- 
doubtedly carbonic  acid  ;  for  it  is  chiefly  this  compound  which  in 
the  deep  region,  under  high  temperature  and  pressure,  develops  a 
greater  solvent  power  for  most  of  the  elements  of  the  rocks.  The 
alkalies,  earths  and  silica  of  our  mineral  springs  have  certainly  been 
dissolved  from  the  rocks  by  carbonic  acid,  and  the  carbonates  thus 
formed  usually  predominate  over  the  associated  sulphates.  The 
analyses  do  not  give  us  the  conditions  in  which  they  exist,  because 
the  statements  of  results  depend  largely  upon  the  individual  views 
of  the  analysts. 

The  general  exhibit  sketched  above  shows  that  in  the  Comstock 
waters  the  sulphates  exceed  the  carbonates,  and  that  the  chemists 
have  been  led  to  connect  the  sulphuric  acid  preferably  with  the 
earths.  They  have  simply  found  an  excess  of  sulphuric  over  car- 
bonic acid,  as  is  the  case  also  in  the  strong  thermal  springs  of  Bohe- 
mia. The  relation  between  the  two  analyses  of  Sulphur  Bank 
water  is  remarkable;  one  showing  the  sulphates,  and  the  other  car- 
bonates, to  be  predominant.  Apparently  one  sample  was  taken 
from  water  which  had  been  for  a  considerable  period  in  contact  with 
the  atmosphere,  so  that  the  liberated  H2S  gas,  oxidizing  to  H2SO4, 
expelled  the  CO2  from  a  part  of  the  carbonates.  The  three  irruptive 
thermal  waters,  Nos.  1,  2  and  3  in  the  table  are  acid,  and  also  contain 
a  notable  quantity  of  free  CO2  in  solution — which,  indeed,  deter- 
mines their  acid  character.  I  have  added  for  comparison  Nos.  16  and 
17,  two  favorite  Bohemian  acid  springs.  No.  18  is  the  famous  Vichy 
spring  in  France;  No.  16  is  a  weak  water,  esteemed  for  table-use; 
and  No.  17  is  the  celebrated  stronger  water  of  Bilin.  A  few  years 
ago,  the  quantity  of  the  latter  spring  had  seriously  fallen  off;  and 
there  is  reason  to  surmise  that  a  part  of  its  water  had  found  a  way 
into  the  collieries  of  Briix,  where  similar  acid  springs  appear  at  seve- 
ral points.  Fortunately  for  Bilin,  an  increased  supply  was  obtained 
there  by  means  of  an  adit  and  bore-hole.  It  is  known  that  distilled 
water  at  normal  barometric  pressure  and  ordinary  indoor  tempera- 
ture may  contain  in  absorption  an  equal  volume  of  carbonic  acid,  and 
that  mineral  water  under  the  same  conditions  has  a  somewhat  higher 
absorption-coefficient.  The  free  CO2,  not  held  in  bicarbonates,  is 
mostly  given  by  analysts  in  terms  of  weight.  These,  by  the  em- 
ployment of  the  well-known  volume  of  one  gramme  of  CO2,  could 
be  easily  transferred  into  terms  of  volume,  a  more  practical  form  for 
all  cases,  which  is  unfortunately  not  yet  generally  used. 


42  THE   GENESIS   OF   ORE-DEPOSITS. 

Since  in  the  deep  regions  the  absorption-capacity  of  water  for  CO2 
is  diminished  by  increased  temperature,  but,  on  the  other  hand,  in- 
creased in  much  greater  proportion  by  increase  of  pressure,  a  portion 
of  the  gas  absorbed  in  depth  is  liberated  in  the  higher  region  and 
contributes  energy  to  the  ascending  current. 

Thus  far  the  substances  present  in  mineral  waters  in  the  largest 
proportions  have  been  chiefly  considered.  We  must  now  study  also 
those  which  occur  in  minute  proportions,  since  these  concern  most 
nearly  the  question  with  which  we  are  dealing. 

Minute  Metallic  Admixtures  in  Mineral  Waters. — Ordinary  analyses 
show  the  presence  of  some  metals,  especially  iron  and  manganese, 
which  occur  as  easily  oxidizable  protoxides,  giving  rise  to  the  pre- 
cipitation of  hydrated  peroxides.  Lime  carbonate,  in  solution  as 
bicarbonate,  is  simultaneously  precipitated  by  evaporation  and  the 
loss  of  CO2 ;  and  silica  is  likewise  thrown  down  under  certain  con- 
ditions. Such  precipitates  are  called,  according  to  their  predominant 
ingredients,  ocher,  sinter,  tufa,  travertine,  etc. 

Minute  metallic  admixtures  are  found  : 

1.  Dissolved  in  the  mineral  water  itself. 

2.  In  the  ochers  or  sinters  deposited  at  the  mouths  of  springs, 
where  they  are  concentrated  in   observable  quantity,  having  been, 
without  doubt,  originally  held  in  solution  by  the  springs. 

3.  Moreover,  there  are  found,  in  some   places,  at  the   mouths  of 
springs,  substances  which   were  not  originally  in   the  solution,  but 
have  been  subsequently  dissolved  and  ultimately  precipitated  by  the 
action  of  the  mineral  water   upon  various  foreign  bodies  attacked 
by  it. 

The  proportions  of  metallic  ingredients  found  in  ordinary  spring- 
analyses  were  at  first  generally  regarded  with  doubt,  unless  a  chemist 
of  the  rank  of  Berzelius  vouched  for  them.  Fresenius  and  others 
admitted  that  such  ingredients  might  be  taken  up  from  metallic  con- 
duits. But  at  last  they  were  proved  to  exist  in  springs,  excluding 
this  hypothesis.  Of  course,  "  traces"  are  worthy  of  less  confidence 
than  ponderable  quantities.  According  to  Dr.  Loschner,*  Gottl 
found  in  the  Giesshiibl  waters  "  traces  "  of  copper,  and  even  of  gold. 
Of  the  fifty-nine  chemical  elements  recognized  in  1817,  twenty- 
four  were  known  to  Elie  de  Beaumontf  as  occurring  in  mineral 
springs.  Of  these  only  six  (Ur,  Mn,  Fe,  Bi,  Sb,  As)  were  metals. 


*  Badeschrift  iiber  Giesshubl,  3  Aufl.  Prag  ,  1855. 

f  Bulletin  de  la  Soc.  GeoL  de  France,  2  Ser.,  iv.,  p.  1 249,  etc. 


THE   GENESIS   OF   ORE-DEPOSITS.  43 

G.  Bischof  *  doubled  this  list,  and  the  knowledge  of  the  subject  has 
been  greatly  increased  since  by  Liebig,  Will,  Fresenius,  Ramrnels- 
berg,  Wackenroder,  Thenard  and  Chevalier.  It  is  chiefly  from  the 
deposits  of  springs  that  we  learn  of  the*  minute  metallic  substances 
once  dissolved  in  them.  The  oxides  of  Cu,  Sn,  Co,  Zn,  Sb,  Ni,  etc., 
were  precipitated  together  with  the  oxide  of  iron.  Ochers  are  es- 
pecially rich  in  arsenic.  Tin  is  often  found  in  the  thermal  deposits 
of  Wiesbaden,  Soden,  Homburg,  Rippoldsau,  Alexisbad,  Driburg, 
Bruckenau,  Kissingen,  etc. 

Lead  occurs  in  the  springs  of  Rippoldsau  (according  to  Will,  1.6 
to  3.7  milligrammes  per  ton),  Kissingen  (10  to  13  mg.  per  ton) 
Alexisbad,  Ems,  Homburg,  Carlsbad  (in  the  Schlossbrunn,  accord- 
ing to  Gottl),  Pyrmont,  etc.f  Copper  has  long  been  known  to  exist 
in  acid  mine-waters  (e.  g.,  the  cement-waters  of  Schmollnitz,  Her- 
rengrund  in  Hungary,  etc.),  and  is  found  also  in  ascending  waters  at 
Carlsbad  (authority,  Gottl),  Aachen  (Liebig),  Bagn£res  de  Luchon 
(Filhol),  Bourbonne  (Tomsier),  Luxueil  (Braconnot,  Henry),  Wies- 
baden (Fresenius),  Bruckenau  (Keller),  Rippoldsau  (Will),  and  in 
many  other  chalybeate  waters. J  Arsenic  is,  of  course,  often  found 
in  mineral  waters.  I  will  mention  only  the  Magdalena  spring  of 
Mont-Dore  (45  to  55  grammes  per  ton,  says  Thenard),  St.  Hectaire 
(6  to  8  per  ton),  Roy  at  (35  g.  per  ton),  and  Bourbole  (815  g.  per 
ton).  G.  Bischof  §  gives  as  follows  the  maxima  found  in  mineral 
springs  up  to  1854: 

Milligrammes  per  Ton. 

Of  Water.  Of  Ocher. 

Arsenious  acid,        .        .        <        .        .        .1.5  38.460 

Antimony  oxide,      .         .         .         .         .         .0.1  

Zinc  oxide  (sulphate), 13.3  

Lead  oxide, 0.1  1.900 

Copper  oxide, 6.4  1.000 

Tin  oxide, 0.1  .50 

I  add,  as  illustration,  the  contents  of  the  mineral  waters  of  two 
important  localities,  as  calculated  from  the  contents  of  the  ocher. 
The  chief  constituents  of  these  waters  are  given  in  the  table  on 
page  38.  The  first  three  springs  are  at  Rippoldsau. 


*  Lehrb.  d.  Chem.  Geologic,  Aufl.,  i.,  p.  2078. 
t  Dr.  B.  M.  Lersch,  Hydrochemie,  i ,  Berlin,  1864,  p.  432. 
J  Ibid.,  p.  438. 

\  Dr.  H.  Ludwig's  Die  naturlichen  Wasser.     Erlangen,  1862,  p.  96.     Compare 
J.  Roth's  Allyemeine  Chem.  Geologic,  Berlin,  1879,  p.  564,  etc. 


44 


THE   GENESIS   OF   ORE-DEPOSITS. 


LOCALITY  : 

Rippoldsau  (ace.  to  WILL.)    Kissingeu  (ace.  to  KELLER.) 

Springs  : 

Josef. 

Wenzel. 

Leopold. 

Pandur. 

Rakoczy. 

Constituents, 

Milligrammes  per  ton. 

25 
16 
104 
600 

17 
10 
69 
400 

38 
24 
156 
900 

134 
107 

128 
1120 

166 
134 
150 

800 

Antimony  oxide 

Copper  oxide 

Arsenious  acid 

In  discussing  Steamboat  Springs  I  have  already  mentioned  the 
metals  found  by  G.  F.  Becker,  among  which  are  Hg,  Au,  and  Ag. 

I  would  only,  in  addition,  call  attention  to  the  variations  in  the 
deposit  of  one  and  the  same  spring,  for  which  purpose  I  select  the 
Puits  de  P  Enclos  des  Celestines,  at  Vichy,*  of  which  an  analysis 
is  given  in  the  table  on  page  38.  This  contains  in  1000  parts : 


Residuum  obtained  by 
evaporating   the 
mineral  water. 

Alkaline  carbonates,  .        .        .      735 
Earthy  carbonates,      .         .        .129 
Ferrous  carbonates,    .         .     "  ''',          3 
Manganous  carbonates,       
Iron  oxide,         
Alkaline  sulphates,     ...        42 
Chlorides,          ....        72 
Silica          8 

Arsenic  acid, 
Other  constituents, 

0.4 
.  v        10.6 

1000.0 


Ochreous 
deposit. 


169 


474 


10 

70 

277 

1000 


Calcareous 
deposit. 


980 

4 

10 


1000 


Alterations  Produced  by  Mineral  Springs. — Daubree,  in  the  chap- 
ters devoted  to  this  subject,  distinguishes  the  action  of  mineral 
waters  upon  the  rock  they  traverse,  and  their  action  upon  artificial 
substances  which  have  found  their  way  into  the  mineral  water.f 

a.  Under  the  first  head  he  cites  al unite,  kaoline,  and  serpentine 
as  the  result  of  mineral  springs  in  general.  I  would  call  attention, 
however,  to  the  circumstance,  not  yet  sufficiently  appreciated,  that 
the  rocks  in  the  neighborhood  of  a  mineral  spring  often  have  a  very 
different  appearance  from  those  at  a  distance.  In  the  case  of 
springs  carrying  sulphuretted  hydrogen,  this  is  self-explanatory. 

*  Dr.  H.  Lud wig's  Die  natilrlichen  Wasser,  Erlangen,  1862,  p.  199. 
f  Les  eaux  souterraines  a  V  epoque  actuelle,  ii.,  p.  67,  and  Les  eaux  souterraines  aux 
epoques  anciennes,  p.  178. 


THE   GENESIS   OF   ORE-DEPOSITS.  45 

Sulphur  Bank  represents  the  phenomenon  in  a  striking  way  as  re- 
gards basalt.  Granite  is  often  decomposed  in  the  neighborhood  of 
springs, — as  in  the  Carlsbad  region,  where  some  acid  springs,  like 
that  of  Giesshiibl,  emerging  on  the  contact  between  granite  and  the 
overlying  Tertiary  rocks,  have  transformed  the  granite  into  kaoline. 
I  have  observed  similar  decomposition  at  the  springs  of  Johannis- 
bad,  in  Bohemia,  and  at  many  other  places.  It  is  to  be  regretted 
that  these  phenomena  have  been  seldom  studied,  as  yet,  from  a 
chemical  standpoint. 

Daubree  has  pointed  out  the  effect  of  mineral  water  upon  various 
rocks  and  artificial  building-materials  in  the  masonry  shafts  of  the 
springs  at  Plombieres  and  Bourbonne-les-Bains  ;*  for  instance,  the 
zeolites  (chabazite,  harmotome,  christianite,  mesotype,  apophyllite) 
formed  in  the  Roman  beton  ;  the  hydrous  silicates  (plombierite, 
chalcedony,  hyalite)  in  the  Roman  bricks  at  Plombieres  ;  recent 
formations  of  calcite  and  aragonite,  and  also  the  funnel-shaped 
cavities  eaten  out  of  the  dressed  limestone  of  the  masonry.  The 
latter  are  specially  interesting  as  having  been  excavated  from  below 
upwards, — that  is,  in  the  direction  of  the  ascending  spring.  Fig.  9 
illustrates  this  action  upon  such  a  building  stone. 

An  analogous,  and,  for  our  purpose,  still  more  important  observa- 
tion, was  made  in  1845,  at  Burtscheid,  near  Aachen,  by  J.  Nog- 
gerath.  A  terrace  was  constructed  at  that  time  in  the  neighborhood 
of  the  hot  spring,  as  the  site  for  a  house.  Blasting  in  the  Devonian 
limestone  exposed  several  vertical  channels  of  nearly  circular  section 
and  20  to  90  centimeters  (8  to  35  inches)  diameter,  some  of  which 
contained  thermal  water  and  emitted  steam.  They  had  been  partly 
choked  by  rock-d6bris,  but  one  of  them  showed  a  depth  of  about  4 
metres  (13  feet).  Immediately  around  these  tubes  the  elsewhere 
solid  limestone  had  been  altered  for  a  distance  of  15  centimeters 
(6  inches)  to  a  gray,  earthy  mass,  almost  plastic  when  damp,  and 
separable  in  thin  scales.  In  places,  this  earthy  mass  had  fallen 
away,  and  on  the  sides  of  the  enlargements  of  the  tube  thus 
formed,  crusts  of  white  lime-sinter  had  been  deposited. f  Noggerath 
does  not  doubt  in  the  least  that  the  mineral  water  emerged  5  to  6 
metres  (16  to  20  feet)  above  the  present  exit,  and  eroded  the  chan- 
nel for  itself.  He  believes  even  that  the  channels  of  all  the  mineral 

*  Experimental  Geology,  p.  82. 

f  J.  Noggerath,  "  Ueber  die  sogenannten  natiirlichen  Schachte  oder  geologischen 
Orgeln  in  verschiedenen  Kalksteinbildungen."  Karsten's  Archiv.  fur  jj/ro.,  Geogn., 
u.  Berybau,  1845,  p.  513. 


46  THE   GENESIS   OF   ORE-DEPOSITS. 

springs  of  Burtscheid  and  Aachen,  which  came  from  the  limestone, 
have  a  similar  shape. 

He  calls  attention  to  the  fact,  observed  by  him  and  his  friend  G. 
Bischof,  that  the  slabs  of  black  marble  covering  the  curbing  of  the 
Kaiserquelle,  near  Aachen,  and  the  Schwerdbad,  at  Burtscheid,  had 
been  transformed  by  the  constant  action  of  the  steam  upon  their 
inner  surfaces  into  a  doughy  mass,  which  could  be  easily  scratched 
away  with  the  finger-nail. 

Besides  this  evident  action  of  thermal  springs  upon  limestone,  we 
may  conclude  from  the  foregoing  that  such  waters,  tending  to  an 
upward  movement,  may  actually  eat  their  way  through  limestone 
to  the  surface,  or  to  rocks  offering  communication  with  the  surface. 
This  circumstance  was  not  known  to  me  when  I  published  my 
monograph  on  the  Rezbanya  deposits,*  in  which  I  attributed  to 
ground-water  the  erosion  of  the  channels  in  the  limestone  which  are 
filled  with  ore,  instead  of  allowing  them  to  have  been  formed  by  the 
ascending  mineral  waters. 

The  treatise  of  Noggerath  above  cited  contains  also  observations 
upon  the  analogy  between  the  thermal-water  channels  of  Burtscheid, 
the  so-called  "geological  organ-pipes"  (les  orgues g&ologiques)  in  the 
chalk-deposits  of  Maestrich,  and  the  "  natural  shafts"  (puits naturels) 
in  the  Eocene  limestone  of  the  vicinity  of  Paris.  The  latter,  however, 
have  shown  neither  mineral  water  nor  any  traces  of  its  former  pres- 
ence, and  are  of  little  interest  for  us.  Recent  investigations  of  both 
the  phenomena  referred  to  are  unfortunately  not  now  at  hand. 

b.  Regarding  the  effects  of  mineral  waters  upon  artificial  products 
immersed  in  them,  we  are  indebted  to  Daubree  for  the  preservation 
of  numerous  important  observations  in  the  masonry  pits  of  the 
springs  of  Plombieres  and  Bourbonne-les-Bains.f 

The  springs  of  Plombieres  occur  in  the  neighborhood  of  ore-bear- 
ing quartz  veins,  and  furnish  at  68°  C.  a  water  rich  in  carbonic  acid 
but  poor  in  solid  constituents,  the  residuum  after  evaporation  being 
400  grammes  per  ton  (0.04  per  cent.).  Those  of  Bourbon  ne-les- 
Bains,  on  the  other  hand,  have  a  temperature  of  58°  C.,  and  are  rich 
in  mineral  matter,  the  residuum  being  7000  to  8000  grammes  per 
ton  (0.7  to  0.8  per  cent),  chiefly  sodium  chloride  (5.800  grammes). 

*  Geol.-mont.  Studie  der  Erzlagerstdtten  von  Eezbdnga  in  S.  0.  Ungam.,  Budapest, 
1874,  p.  179. 

f  li  Formation  contemporaine  de  diverges  esp£ces  minerals  cristallises  dans  la 
source  thermale  de  Bourbonne-les- Bains."  Annales  des  Mines,  6  series,  1875,  viii., 
p.  439.  Also,  the  German  edition  of  DaubreVs  Etudes  syntheligues,  1880,  p,  57. 


THE   GENESIS   OF   ORE-DEPOSITS.  47 

They  flow  from  the  variegated  marls  of  the  upper  Trias,  underlying 
the  Muschelkalk,  in  the  vicinity  of  large  fault- fissures.  Carbonic 
acid  appears  to  be  present  in  traces  only,  and  the  same  is  true  of  hy- 
drogen sulphide,  which  is  detected  by  its  odor,  and  has  given  rise 
also  to  small  deposits  of  sulphur. 

In  1874,  with  the  aid  of  powerful  pumps,  the  abundant  current  of 
the  spring  was  successfully  overcome,  and  the  foundation  of  the  old 
Roman  curbing  was  made  accessible.  The  mineral  water  rises  from 
horizontal  clay  beds  through  a  funnel  filled  with  sand,  which  scarcely 
represents  the  original  channel.  At  the  bottom  of  the  masonry  lining 
a  clayey  slime  was  encountered,  in  which,  besides  thousands  of  hazel- 
nuts,  acorns  and  fruit-seeds,  many  Gothic  and  Roman  coins  were 
found,  with  numerous  other  objects,  such  as  bronze  statuettes,  needles, 
rings  of  electrum,  pieces  of  leaden  framing,  etc.  The  gold  coins 
weighed  in  all  25  grammes,  the  silver  coins  625  grammes,  but  of  the 
bronze  coins  there  were  20,800  grammes,  and  many  had  disappeared 
entirely,  leaving  only  their  impress,  and  forming  shapeless  masses  of 
the  products  of  their  decomposition,  mixed  with  grains  of  sand.  Of 
the  minerals  formed  from  the  bronze,  the  greater  part  came  from  the 
copper  (red  copper-ore,  copper-glance,  chal  copy  rite,  peacock-ore, 
tetrahedrite,  atacamite,)  and  only  one  from  the  tin — on  a  coin  which 
still  showed  bronze  in  its  interior,  but  was  covered  with  a  white 
layer  of  tin  oxide.  The  action  upon  lead  had  produced  coatings  of 
galena  and  phosgenite,  scales  of  lead  oxide,  and  cerussite.  Iron 
had  not  been  altered  to  ordinary  rust ;  the  product  of  its  oxida- 
tion contained  silica.  Moreover,  pyrite,  instead  of  the  earthy  black 
sulphide  often  occurring  on  the  surface,  had  been  formed  from  the 
iron,  and  was  found  covering  pebbles  and  grains  of  quartz,  angu- 
lar fragments  of  sandstone,  and  also  some  evidently  artificial  pro- 
ducts, such  as  flint  knives — thus  indicating  indubitably  its  recent 
origin. 

Strange  to  say,  in  spite  of  the  quantity  of  chlorides  in  the  water, 
and  the  great  affinity  of  silver  for  sulphur,  the  silver  coins  had  not 
been  very  seriously  attacked,  and  their  designs  were  still  quite  dis- 
tinct, when  they  had  not  been  coated  with  sulphides  from  the  neigh- 
boring bronze  coins.  They  must  have  been  protected  from  chem- 
ical action  by  something  not  now  determinable. 

Moreover,  iron  and  silica  (or  a  hyd rated  silicate)  had  penetrated 
the  wood  found  in  the  springs. 

"  At  Bourbonne,  as  at  Plombieres,  the  intrusive  formations  a  re  less  than  8 
meters  (28  feet)  below  the  surface ;  and  yet  they  are  very  different  from  what  we 


48  THE   GENESIS   OF   ORE-DEPOSITS. 

are  accustomed  to  see  in  our  laboratories.  A  temperature  was  sufficient  for  them 
which  'is  low  in  comparison  with  that  which  obtains  at  greater  depths.  What 
forces  would  we  not  see  at  work,  if  we  were  permitted  to  follow  downward  the 
channels  which  have  been  the  pathway  of  hot  springs!" — Daubre*e,  op.  cit.> 
p.  91. 

Structural  Features  of  the  Deposits  of  Mineral  Springs. — The 
original  conditions  at  the  point  of  outflow  of  mineral  springs  have 
seldom  been  preserved  intact.  Even  when  their  channels  have  been 
successfully  prolonged  through  the  ground-water  to  the  surface, 
erosion,  on  the  one  hand,  has  partially  removed  them  (since  they 
often  emerge  in  valley-bottoms),  or  human  agency  on  the  other 
hand,  has  variously  disturbed  them  by  diverting,  choking,  or  wall- 
ing them,  or  by  the  erection  of  buildings  with  foundations.  For 
our  purpose  it  is  important  to  be  able  to  show  that,  in  all  channels 
extending  to  the  surface  and  still  uninjured,  a  regular  filling  with 
symmetrically  arranged  mineral  crusts  may  be  observed. 

Such  a  regular  filling  of  the  fissure-channel  of  a  spring  I  have 
seen  at  the  tufa  mounds  of  the  Bad  of  Arczo  near  Parajd  in  Transyl- 
vania.* The  filling  of  a  fissure  25  centimeters  (10  inches)  consists 
of  variegated  crusts  of  aragonite,  as  thin  as  paper,  the  fibers  of  which 
are  perpendicular  to  the  walls  of  the  channel.  The  latest  crusts  are 
darker,  and  give  a  bituminous  odor  when  dissolved  in  hydrochloric 
acid ;  the  oldest  are  usually  milky  white,  and  leave  after  similar 
treatment  a  residuum  of  gelatinous  silica.  The  water  tastes  very 
unpleasantly  salt  and  bitter.  The  gas  which  hisses  from  the  depths 
of  the  fissure  is  doubtless  mainly  carbonic  acid,  perhaps  with  an 
admixture  of  hydro-carbon. 

Since  the  drawing  of  the  mouths  of  Steamboat  Springs  given  by 
Le  Conte  (op.  tit.,  p.  423)  may  not  be  entirely  comprehensible,  I 
introduce  in  Fig.  8  an  ideal  section  of  one  of  the  spring-mounds 
of  Arcz6. 

It  is  only  the  channel  which  is  filled  with  solid,  almost  transpar- 
ent crusts;  the  deposits  on  the  side  of  the  mound  are  a  fine-grained, 
white  lime  mass,  and  in  the  less  immediate  vicinity  of  the  springs 
there  are  in  many  places  horizontal  layers  of  a  lime  tufa,  containing 
plant-remains.  , 

Pigeon  and  Voisin  describe  an  analogous  but  much  larger  phe- 
nomenon in  Vichy,  at  the  rocher  des  Celestins,  where  an  almost  ver- 

*F.  Posepny.  "Studien  aus  dem  Salinargebiete  Siebenbtlrgens,"  Jahrb.  d.  k.  k. 
geol.  Reichsanstalt,  Vienna,  1867,  xvii.,  p.  477. 


THE   GENESIS   OF   ORE-DEPOSITS.  49 

tical  aragonite  filling,  2  meters  (6.5  feet)  wide  and  200  meters  (650 
feet)  long,  with  fibers  perpendicular  to  the  planes  of  the  crusts,  may 
be  observed  (Daubree,  op.  cit ,  p.  159). 

The  waters  flowing  away  from  mineral  springs  likewise  make 
sojid  deposits,  which  often  form  horizontal  layers,  covering  consid- 
erable areas.  These  are  the  so-called  travertines — formations  analo- 
gous to  the  Carlsbad  Sprudel-  or  Erbsenstein,  etc.  But  we  are  con- 
cerned at  this  point  with  the  deposits  in  the  spring-channel  itself 
and  in  its  immediate  vicinity,  including  not  merely  the  crusts  upon 
the  walls  proper,  but  also  those  surrounding  large  or  small  frag- 
ments of  rock  within  the  channel.  Many  such  deposits  are  charac- 
terized by  the  pisolite  formation,  which  we  may  observe  also  in  ore- 
deposits  (concretionary  iron-ores,  etc.).  These  pisolites  are  evidently 
incrusted  kernels,  the  crusts  being  proportionately  much  thicker  than 
the  kernels.  The  Carlsbad  Sprudehtein  shows,  indeed,  the  same 
structure  on  a  small  scale  as  many  ore-deposits  exhibit  on  a  large 
scale.  The  pisolites,  like  those  of  Tivoli  and  Hamman  Meskoutine, 
consist  of  lime  carbonate,  pure  or  slightly  intermixed  with  iron 
oxide  and  silica.  At  the  last-named  locality  pyrite  occurs  between 
the  layers  of  carbonate,  so  that  the  formation  must  be  pronounced  to 
be  crusts  of  lime  carbonate  and  pyrite  upon  a  foreign  nucleus,  which 
was  elevated  and  incrusted  so  long  as  the  ascending  column  of  the 
spring  had  energy  enough  to  move  it. 

A  few  words  may  be  well  added  here  concerning  the  Carlsbad 
Sprudelschale  and  Erbsenstein.  As  is  well  known,  the  Sprudfl  rep- 
resents an  action  like  that  of  geysers,  ejecting  thermal  water  and5 
steam  to  a  considerable  height.  The  precipitate  at  the  present  time 
is  a  porous,  somewhat  ferruginous  aragonite  or  travertine  mass. 
The  ground  from  which  the  Sprudel  breaks  forth  is  composed  of  hori- 
zontal layers  of  a  much  denser  aragonite  mass,  which  can  be  pol- 
ished, and  furnishes  material  for  artistic  lapidary-work.  A  part  of 
the  town  of  Carlsbad  stands  on  this  so-called  Sprudelschale,  from 
which  new  thermal  springs  sometimes  break  out,  and  the  structural 
history  of  which  may  have  been  like  that  of  the  rising  succession  of 
basins  at  the  Mammoth  Hot  Springs  of  Gardiner  river,  in  the  Yel- 
lowstone National  Park. 

Certain  layers  of  this  Sprudel- deposit  are  exclusively  aggregates  of 
pisolites  of  pea-size,  whence  the  name  Erbsenstein  (pea-stone).  Evi- 
dently these  have  been  formed,  like  those  of  the  Hamman  Meskou- 
tine spring,  immediately  at  the  outflow  of  the  mineral  water.  The 
precipitate  from  the  solution  (at  the  moment  supersaturated)  was  de- 

4 


50  THE   GENESIS   OF   ORE-DEPOSITS. 

posited  around  individual  rock-grains,  which  had  found  their  way 
into  the  spring,  to  be  for  awhile  kept  in  motion  by  its  current.  Suc- 
cessive crusts  were  thus  deposited,  until  the  pisolite  became  too  large 
to  follow  the  movement  of  the  spring  and  sank  to  the  bottom,  where 
its  accessible  surfaces  received  still  further  precipitate-crusts.  It 
might  easily  occur,  that  single  cavities  might  remain,  into  which  the 
precipitate  could  not  penetrate.  These  would  represent,  according 
to  our  terminology,  the  central  druse.  Fig.  12  illustrates  this  pro- 
cess, while  Fig.  13  shows  a  single  pisolite,  including  pyrite-crusts, 
from  Hamman  Meskoutine. 

I  have  had  opportunity  to  see  a  completely  analogous  result  pro- 
duced by  falling  drops  at  Offenbanya,  where,  at  certain  points  in  an 
adit  abandoned  for  some  thirty  years,  water  rich  in  lime  carbonate 
trickled  from  the  roof,  forming  upon  the  floor  a  deposit  several  cen- 
timeters thick.  At  the  spot  where  the  drops  fell  directly  upon  the 
floor,  a  small  basin-like  depression  was  formed,  in  which  lay,  like 
eggs  in  a  birds'  nest,  various  bodies  like  pisolites,  consisting  of  a 
sand-grain  at  the  center,  surrounded  by  concentric  crusts  of  car- 
bonate. Some  of  these  formations  lying  in  the  middle  of  the  nest 
were  quite  loose,  so  that  they  were  turned  over  by  the  force  of  the 
falling  drops,  which  explained  the  tolerably  uniform  incrustation 
upon  them.  Others  situated  near  the  edge  were  already  fixed,  could 
not  move  any  longer,  and  showed  at  points  a  deposit  of  sinter*  (Figs. 
14  and  15).  Similar  formations,  known  as  "  birds'  nest,"  are  de- 
scribed by  Schmidt  in  the  old  mine-workings  of  Riegelsdorf  and 
Bieber.f  Such  formations  appear  to  be  by  no  means  rare  in  metal- 
mines.  I  found,  for  instance,  in  Offenbanya  at  the  face  of  a  level 
which  had  been  abandoned  for  some  years,  that  small  chips  of  rock 
had  been  covered  by  the  falling  drops  with  two  separate  thin  crusts: 
first,  a  white  lustrous  smithsonite,  and  thereupon  a  black,  easily- 
detached  crust  of  a  maganiferous  substance.^  (Fig.  16).  The  piso- 
litic  bodies  formed  by  falling  drops  are  not  easily  confounded  with 
those  formed  by  a  flowing  spring,  and  when  such  are  found  in  the 
interior  of  an  ore-filling,  they  cannot  well  be  ascribed  to  drippings. 

Pisolitic  forms  appear  in  many  ore-deposits.  Thus  the  calamine- 
deposit  of  Santander  in  Spain  betrays  an  oolitic  structure,  and  I 
have  observed  in  the  gold  mines  of  Verespatak,  pisolitic  forms,  the 

*  F.  Posepny,  "  Ueber  concentrisch-schalige  Mineralbildungen,"  k.  Akad.d.  Wis- 
sensch,  Vienna,  1868. 

f  Beitrage  zu  der  Lehre  von  den  Gangen,  p.  42. 

J  See  my  paper  on  crustified  mineral  formations,  cited  above. 


THE   GENESIS   OF   ORE-DEPOSITS.  51 

kernel  being  an  aggregation  of  gold,  and  the  surrounding  thin 
crusts,  carbonates  of  lime,  manganese  and  iron.  To  this  subject  I 
shall  recur. 

From  what  has  been  said  concerning  the  structural  relations  of 
mineral-spring  deposits,  it  appears  that  at  the  mouths  of  such  springs 
phenomena  are  shown,  such  as  crustifications  of  wall-deposits,  piso- 
litic  forms,  etc.,  which  we  meet  frequently  in  ore-deposits  also — an 
additional  reason  for  declaring  the  latter  to  have  been  formed  by 
mineral  springs. 

5.  ORIGIN  OF  ORE-DEPOSITS  IN  THE  DEEP  REGION. 

We  have  seen  that  the  mineral  springs  which  ascend  to  the  sur- 
face are  dilute  metallic  solutions,  and  that  at  their  outflow  (the  only 
point  where  we  can  directly  observe  their  activity)  they  form  deposits, 
containing  metals,  among  other  things,  and  exhibiting  a  structure 
which  occurs  in  ore-deposits  likewise.  We  have  followed  to  a  not 
inconsiderable  depth  one  ore-deposit  which  occurs  upon  an  ascend- 
ing spring,  and  have  found  that,  apart  from  changes  conditioned  by 
the  vicinity  of  the  surface,  it  continues  its  character.  Finally,  we 
have  encountered  mineral  springs  in  many  places  where  mining  has 
followed  ore-deposits  in  depth.  Joining  these  several  links  of  ob- 
servation, we  cannot  avoid  the  conclusion  that  the  ore-deposits  found 
in  the  deep  region  are  the  products  of  mineral  springs,  the  more  so 
since  many  of  them  have  a  structure  and  form  which  can  only  be 
explained  as  the  result  of  precipitation  from  liquids  circulating  in 
channels.  The  deposits  from  these  liquids  contain  substances  which 
are  foreign  to  the  surface  and  to  the  shallow  region,  and  hence  could 
not  have  been  brought  into  circulation  by  the  descending  ground- 
water,  but  must  have  come  from  a  deep  region,  where  higher  tem- 
perature and  pressure  (the  two  factors  increasing  the  solubility  of  all 
substances)  exist. 

Comparing  the  average  density  of  the  earth  (which  is,  according  to 
the  very  recent  and  careful  investigations  of  R.  von  Sterneck,*  5.6) 
with  the  average  density,  2.5,  of  the  rocks  forming  the  earth's  crust, 
we  must  admit  that  in  the  central  mass  substances  much  denser 
than  5.6  have  been  accumulated,  that  is  to  say,  the  deep  region  is 
the 'peculiar  home  of  the  heavy  metals. 

If  we  imagine  ourselves  standing  in  the  deep  region  in  front  of 

*  I  would  call  attention  to  the  labors  of  v.  Sterneck,  pursued  upon  this  point 
for  a  decade,  and  described  in  the  Mittheilungen  des  k.  k.  Militar.  Geograph.  Institutes, 
in  Vienna. 


52  THE   GENESIS    OF   OKE-DEPOSITS. 

the  profile  of  an  ore-lode,  like  the  Adalbert  at  Przibram,  for  instance, 
1110  m.  (3600  feet)  below  the  surface  and  564  m.  (1850  feet)  below 
sea-level,  we  perceive  a  fissure-space  of  discission,  filled  with  sym- 
metric mineral  crusts,  chiefly  argentiferous  lead  sulphide.  Remem- 
bering that  this  filling  has  been  stoped  continuously  to  the  sur- 
face, we  can  find  no  other  satisfactory  explanation  than  the  hy- 
pothesis that  it  was  brought  up  from  still  greater  depths,  and,  in 
view  of  the  comparative  insolubility  and  the  large  quantity  of  the 
metallic  sulphide  here  accumulated,  it  must  have  been  deposited 
from  perpetually  renewed,  and,  therefore,  from  ascending,  mineral 
solutions.  Whoever  has  had  opportunity  to  study  an  ore-lode  in 
the  deep  regions  can  conceive  no  other  explanation.  The  miners 
themselves  have  always  held  this  opinion;  in  other  words,  they  have 
all  been  ascensionists.  In  the  case  of  ore- deposits  occupying  tubular 
channels  in  soluble  rocks,  the  origin  of  these  spaces  is  not  at  once 
clear;  and  it  has  thus  happened  that  one  or  another  observer,  mis- 
understanding the  analogy  of  the  substance  and  the  conditions  of 
filling,  has  suggested  a  different  hypothesis,  as,  for  instance,  S.  F. 
Emmons,  whose  conclusions  as  to  the  Leadville  deposits  I  shall 
take  the  liberty  of  controverting  in  a  later  part  of  the  present  paper. 
I  do  not  deny  that  there  are  ore-deposits  permitting  such  a  different 
explanation,  but  they  occur  in  the  shallow  region  only,  and  not  in 
the  deep  region. 

In  the  two  groups  of  ore-deposits  already  discussed,  and  formed 
in  pre-existing  spaces,  a  distinct  crustification  leaves  no  doubt  as  to 
the  manner  of  filling.  Where  crustification  is  obscure  or  absent, 
it  is  indeed  not  possible  at  once  to  offer  this  convincing  proof  of  the 
manner  of  deposition.  Recourse  must  then  be  had  to  the  analogy 
of  the  substances  and  their  paragenesis.  If  these  correspond  with 
the  contents  of  spaces  filled  with  crusted  deposits,  a  similar  origin 
must  be  inferred  ;  that  is  to  say,  even  in  cases  in  which  mineral  so- 
lutions, ascending  from  the  deep  region,  found  no  open,  continuous 
channels,  but  were  forced  to  create  the  necessary  space  by  the  re- 
moval of  a  previously-existing  material,  the  conditions  of  the  deep 
circulation  still  controlled.  From  these  considerations  it  follows 
that  all  the  deposits  of  the  deep  region  are  referable  to  one  general 
ruling  process,  clearly  shown  to  be  the  action  of  ascending  mineral 
solutions ;  that  is,  they  were  all  formed  by  ascension. 

This  conception  is  diametrically  opposed  to  the  view  recently 
suggested  by  Dr.  F.  Sandberger,  that  ore-deposits  are  formed  by 
so-called  lateral  secretion.  This  view  was  at  first  asserted  to  be 


THE   GENESIS   OF   ORE-DEPOSITS.  53 

universally  applicable.  Afterwards,  the  author  characterized  it  as 
holding  good  for  the  majority  of  ore-veins  only,  and  restricted  it 
by  the  following  definition  : 

"  The  theory  of  lateral  secretion  was  conceived  in  this  sense  only,  that  the 
material  for  the  filling  of  veins  is  derived  from  the  country-rock  through  gradual 
leaching  by  seepage-water  (Sickerwasser),  which  brings  the  dissolved  substance 
from  both  sides  to  the  vein-fissure,  where  it  is  then  converted  by  chemical  decom- 
positions into  insoluble  gangue-minerals  and  ores,  and  so  deposited."* 

It  will  be  seen  that  he  started  from  the  wholly  erronibus  assump- 
tion that  the  ore-veins  of  the  deep  region  stood  open  (like  the 
fissures  in  a  rock  upon  the  surface),  so  that  seepage-water  from  both 
sides  could  deposit  material  in  them.  That  is,  he  conceived  of  a 
fissure  containing  air  only,  and  forgot  entirely  that  such  open 
fissures  are  found  exclusively  above  the  ground-water  level,  below 
which  every  newly-formed  fissure  must  be  immediately  filled  with 
water.  The  term  sickern  corresponds  with  the  English  "seep/' 
"  trickle,"  or  "  drop/7  and  can  only  be  understood  as  describing  the 
downward  movement  of  a  small  quantity  of  liquid.  It  is  thus  im- 
possible to  suppose  that  Sandberger's  meaning  has  been  misunder- 
stood ;  and  we  are  forced  to  conclude  that  he  boldly  extended  his 
conclusions  to  cover  a  region  with  the  physical  conditions  of  which 
he  was  unacquainted. 

A  lateral  secretion  in  this  sense  is,  as  I  have  elsewhere  shown,f 
possible  above  the  ground -water  level  only.  It  is  indeed  conceiva- 
ble that  even  in  the  deep  region  isolated  spaces  may  exist,  from 
which  accumulated  gases  find  no  way  to  the  surface,  and  in  which 
formations  may  occur,  similar  to  those  in  cavities  above  water-level ; 
but  such  instances  (as  at  Wiesloch,  in  Baden,  and  Raibl,  in  Carinthia) 
are  demonstrably  exceptions  to  the  general  rule  above  stated. 

What  interests  us  most  is,  that  in  order  to  establish  his  theory, 
Sandberger  was  forced  to  discredit  the  fact  of  actual  deposition  in 
the  channels  of  mineral  springs.  The  proof  of  this  fact  at  Sulphur 
Bank  and  Steamboat  Springs  was  highly  inconvenient.  Since,  as 
he  had  said,  "  waters  which  flow  with  such  rapidity  as  that  of 
ascending  mineral  springs  containing  carbonic  acid  are  shown  by  ex- 
perience to  produce  no  deposits  in  their  channels,  but  to  do  this 

*  F.  Sandberger,  Uniersuchungen  tiber  Erzgange,  2tes  Heft,  Wiesbaden,  1885,  p. 
159. 

t  "  Ueber  die  Bewegungsrichtung  der  unterirdisch  circulirenden  Flussigkeiten." 
— Comptesrend.  dela  session  da  Congres  gM.  internal.,  Berlin,  1885. 


54  THE   GENESIS   OF   ORE-DEPOSITS. 

only  in  the  immediate  vicinity  of  their  outflow"  (op.  cit.,  p.  5),  he  was 
not  convinced  by  the  conditions  shown  at  Steamboat  Springs,  where 
the  deposits  are  near  the  outflow.  With  regard  to  Sulphur  Bank, 
he  was  not  acquainted  with  the  works  of  Le  Conte  and  G.  F. 
Becker,  showing  that  the  ore-deposit  is  found  in  the  channel  itself. 
Although  he  did  not  doubt  "that  ore-deposits  are  here  observed  in 
process  of  formation "  (/.  c.,  p.  13),  he  recalled  the  well-known 
solubility  of  mercury  sulphide  in  alkaline  sulphides  ;  argued  that 
"the  leaching  of  pre-existing  quicksilver-deposits  by  alkaline  sul- 
phides presents  no  difficulty  "  (/.  c.,  p.  15) ;  and  was  inclined  to 
believe  that  the  cinnabar-deposits  near  the  outflow  were  referable  to 
older  ones.  Endeavoring  thus  to  render  harmless  the  two  instances 
unfavorable  to  the  lateral-secretion  theory,  he  summed  up  his  con- 
sideration of  them  at  that  time  with  the  remark  that  "  in  California 
no  proof  is  presented  of  the  formation  of  ore-veins  by  ascending 
springs"  (op.  cit.,  p.  16).  After  reading  Le  Conte's  account  he  re- 
turned to  the  subject  in  the  second  part  of  his  work,*  asserting  (p. 
162)  that  in  the  numerous  excavations  connected  with  the  walling- 
in  of  mineral  springs,  it  has  never  been  observed  that  hot  springs 
have  deposited  "  metals7'  in  the  immediate  vicinity  of  their  chan- 
nels. He  confesses  again  (p.  161)  that  here  is  "unquestionably  an 
ore-deposit,  formed  by  the  precipitation  of  silica  and  cinnabar  from 
a  hot  alkaline  sulphur-spring,  which  has  found  and  dissolved  mer- 
cury sulphide  somewhere  below;"  and  admits  that  hot  alkaline 
sulphur-waters  may  precipitate,  besides  quicksilver,  also  gold,  tin, 
bismuth,  arsenic,  and  antimony, — but  not  copper,  silver,  and  lead- 
ores,  which  are  often  associated  with  the  foregoing.  These,  he  says, 
cannot  have  been  deposited  from  hot  alkaline  sulphur-springs. 
"There  is,  therefore  (p.  162),  no  reason  in  the  conditions  of  Sulphur 
Bank  for  restoring  the  ascension  theory  to  its  former  authority  in 
the  science  of  ore-veins." 

It  will  be  seen  that  his  chief  argument  is,  that  according  to  his 
opinion,  no  metallic  deposit  has  ever  been  found  in  the  channel  of 
a  spring,  for  he  seems  not  to  consider  as  conclusive  the  deeper 
workings  at  Sulphur  Bank.  Such  a  sweeping  assertion  is  easy;  for 
it  is  not  likely  that  in  walling  a  mineral  spring  excavations  will  be 
carried  deep  enough  to  reveal  the  condition  of  its  channel  proper. 

Sandberger's  contention  comprises  two  propositions :  (1)  Metals 

*  Untersuchunyen  fiber  Erzgtinge,  Wiesbaden.  First  part,  1882 ;  second  part, 
1885. 


THE   GENESIS   OF   ORE-DEPOSITS.  55 

have  been  found  hitherto  only  in  the  ochreous  deposits  from  mineral 
springs;  and  (2)  in  walling  mineral  springs,  deposits  formed  in  their 
channels  have  not  yet  been  found.  These  two  assertions  are  not 
controverted  ;  but  the  conclusion,  that  because  hitherto,  in  digging 
out  mineral  springs,  we  have  found  no  metals  in  their  channels, 
therefore  they  cannot  be  deposited  in  the  channels,  but  only  at  the 
outflow,  is  illogical. 

Excavations  for  the  walling  of  mineral  springs  do  not  extend  to 
the  channels  of  the  deep  region.  Heavy  pumping  is  required  to 
penetrate  even  a  few  meters  below  the  ground-water  level ;  whereas, 
to  decide  this  question,  a  depth  must  be  reached  at  which  the 
ascending  spring  is  not  altered  by  the  descending  ground-water,  the 
oxidation  and  chlorination  due  to  surface  agencies  no  longer  appear, 
etc. 

We  know  that  temperature  and  pressure,  the  two  great  factors  of 
solubility,  are  continually  diminished  as  the  surface  is  approached  ; 
and  we  can  directly  observe  one  result  of  this  change  in  the  libera- 
tion of  the  carbonic  acid  absorbed  at  greater  depths.  Why  should 
not  the  substances  rendered  insoluble  by  the  decrease  of  these 
factors  be  deposited  in  the  channels?  If  no  such  deposition  has 
occurred,  then  the  precipitates  must  have  been  carried  upward  by 
the  current,  and  should  be  separable  by  filtration  from  the  water.  G. 
F.  Becker,  in  filtering  the  Steamboat  Springs  water  before  analysis, 
found  (/.  c.,  p.  346)  in  the  filtrate  a  precipitate  of  antimony  and 
arsenic  sulphides,  with  silica,  which  he  ascribes  to  the  fall  of  tem- 
perature and  the  action  of  low  forms  of  plant-life. 

But  we  find  in  various  closed  conduits  of  mineral  water — i.e.,  in 
artificial  channels — that  deposits  are  formed,  not  only  at  the  mouth, 
but  also  in  the  channel  itself.  Why  should  natural  channels  form 
an  exception  ? 

I  think  it  has  been  shown  that  Dr.  Sandberger's  chief  objection 
to  the  formation  of  ore-deposits  by  ascending  mineral  springs  is 
without  foundation,  and  that  the  entire  chain  of  phenomena  cor- 
roborates our  explanation.  But  the  lateral-secretion  theory  of 
Sandberger  suffers  from  several  other  fundamental  defects,  which  I 
cannot  avoid  indicating  in  this  place,  because  that  theory  was  for  a 
while  accepted  as  a  simple  and  welcome  explanation  of  the  genesis 
of  ore-deposits,  and  began  to  hinder  the  progress  of  knowledge  on 
that  subject. 

It  found  many  disciples,  especially  among  mineralogists,  because 
it  permitted  the  most  extensive  genetic  generalizations,  without 


56  THE   GENESIS   OF   ORE-DEPOSITS. 

requiring  the  observer  to  leave  his  mineral  collection  and  laboratory, 
to  descend  into  the  mine,  and  to  study  the  ore  in  the  place  of  its 
origin.  On  the  other  hand,  it  must  be  confessed  that  the  promul- 
gation of  this  theory  led  to  many  investigations  of  rocks,  which 
will  be  useful  to  science  in  other  directions. 

Sandberger,  being  convinced  that  he  had  detected  foreign  admix- 
tures of  the  metals  in  silicates,  felt  himself  warranted  in  explaining 
by  his  theory  all  ore-deposits  in  the  silicate  rocks ;  but  he  could  not 
so  well  deal  with  those  in  limestone,  which  were  cited  by  Stelzner 
as  a  chief  argument  against  the  universality  of  his  conclusion.* 
With  regard  to  Raibl,  in  Carinthia,  it  occurred  to  him  to  examine 
the  marly  slates  (Mergelschiefer)  overlying  the  limestone;  and  find- 
ing in  these,  besides  traces  of  Li,  Cr,  and  Cu,  more  considerable 
quantities  of  Pb  and  Zn,  he  concluded  that  the  metals  in  the  ore- 
channels  of  the  limestone  under  these  slates  had  been  leached  out  of 
the  latter  (op.  cit.,  p.  34).  This  was  already  a  descending,  and  not 
a  lateral  secretion. 

In  a  paper  upon  the  applicability  to  this  case  of  the  lateral-se- 
cretion theory ,f  however,  I  pointed  out  that  also  below  the  ore- 
bearing  limestone  of  Raibl,  at  Kaltwasser,  there  are  silicate  rocks, 
which  probably  contain  likewise  minutequantities  of  metal,  and  that 
if  Sandberger  had  successfully  analyzed  these,  he  would  have  been 
obliged  to  assume  an  ascent.  In  the  same  paper,  I  argued  that  the 
lateral-secretion  theory  does  not  account  for  the  sulphur  and  the 
metallic  sulphides;  and  I  brought  forward  for  discussion  the  veins 
of  Przibram,  assuming  that  in  that  district,  where  sedimentary  rocks 
are  traversed  by  heavy  eruptive  masses,  Sandberger  could  consider 
the  latter  only  as  the  original  source  of  the  metals  in  the  veins. 
From  average  analyses  for  the  latest  year  of  production,  I  calcu- 
lated that  each  square  meter  (10.75  square  feet)  of  vein-surface 
stoped  represented  190  kilogrammes  (26  I  Ibs.)  of  metallic  sulphides, 
or  in  detail  : 

Pb.          Zn.       Fe.     Cu.         Ag.  S.  Sb.  As. 

Kilogrammes,      132        13        5      0.3        0.8      34.6        2.5        1.7 

If  these  substances  had  been  derived  by  lateral  secretion  from  the 
country-rock  (the  eruptive  mass  being  30  meters  thick  by  the  main 
vein,  or  100  meters  for  the  whole  group  of  veins)  there  must  needs 
have  been  in  each  cubic  meter  (35  cubic  feet)  of  the  country-rock 

*  A.  Stelzner,  Jahrb.f.  Mm.,  1881,  p.  209. 

f  Oesler.  Zitsch.f.  B.  u.  H.  1882,  xxx.,  p.  607. 


THE   GENESIS   OF   ORE-DEPOSITS.  57 

1.9  to  6.3  kilogrammes  (4  to  18  pounds)  of  metallic  ingredients — a 
quantity  not  to  be  called  minute.  Or,  reversing  the  calculation, 
and  starting  with  the  largest  proportion  of  metal  ever  found  in  these 
eruptive  rocks,  it  would  have  required  more  than  one  hundred 
times  the  thickness  of  such  rocks  actually  present  in  the  district 
to  supply  the  contents  of  the  veins.  By  these  calculations  and 
other  arguments,  I  showed,  as  I  thought,  the  special  inapplicability 
of  the  theory  to  Przibram,  but  I  expressed  a  willingness  to  ex- 
amine some  of  the  eruptive  dikes  for  minute  metallic  admixtures, 
preferring  only  that  such  an  examination  should  be  checked  by  an- 
other person. 

The  management  of  the  government  mining  department  en- 
trusted to  the  chemist,  A.  Patera,  the  investigation  of  individual 
samples  of  Przibram  rock,  but  also  called  Dr.  F.  Sandberger  to 
Przibram,  where  the  first  tests  were  executed  with  the  aid  of  a  Com- 
mission, of  which  I  was  a  member.* 

Unfortunately  an  ailment  of  the  eyes  forced  me  to  inactivity,  and 
I  could  do  little  on  the  Commission. 

Dr.  Sandberger  submitted  a  statement  (op.  cit.,  p.  305-327)  or  com- 
pilation, from  which  it  appeared  that  he  attached  less  importance  to 
the  analysis  of  the  eruptive  rocks  than  to  that  of  the  stratified  rocks, 
composed  of  the  detritus  of  the  central  Bohemian  gneiss  mass.  Ac- 
cording to  this  view,  the  metals  of  the  Przibram  veins  came  from 
the  mica  of  the  gneiss  detritus.  According  to  Dr.  Sandberger,  how- 
ever, (op.  cit.,  p.  362-3,)  the  investigation  disclosed  that  "  an  essential 
part  of  the  lead  and  silver  contents  of  the  ore-veins  is  due  to  the 
eruptive  rocks  " — which  involves  a  modification  of  the  above  theory. 

Twenty-five  rock-samples,  selected  by  the  Commission,  were 
tested  for  metallic  admixtures  according  to  a  method  agreed  upon 
(but  not  very  strictly  followed)  by  Dr.  Sandberger,  H.  Freiherr  von 
Foullon,  A.  Patera  and  C.  Mann,  with  tolerably  concordant  re- 
sults, although  Patera  in  particular  expressed  some  doubts  as  to  the 
correctness  of  the  method.  This  led  Prof.  A.  Stelzner  in  Frei- 
bergf  to  make  a  thorough  test  of  the  means  employed,  which  showed 
that  Sandberger's  method  cannot  decisively  determine  whether  the 

*  Untersuchungen  von  Nebengesteinen  der  Przibram er  Gange  rait  Riicksicht 
auf  die  Lateralsecretionstheorie  von  Dr.  F.  V.  Sandberger,  ausgefiihrt  1884-7  und 
veroffentlicht  im  Auftrage  Seiner  excellenz  des  k.  k.  Ackerbauministers  J.  Grafen 
von  Falkenhayn. "— B.  u.  H.  Jahrb.  d.  k.  k.  Bergakad.,  etc.  xxv.,  1887,  p.  299. 

f  A.  Stelzner,  "Die  Lateralsecretionstheorie  und  ihre  Bedeutung  fur  das  Przi- 
bramer  Ganggebiet." — Jahrbuch  der  k.  k.  Bergakad.,  1889,  p.  1. 


58  THE   GENESIS   OF   ORE-DEPOSITS. 

metals  detected  in  the  silicate  were  original  constituents,  or  whether 
they  are  not  secondary  impregnations,  left  undissolved  by  the  reagents 
employed. 

It  is  thus  rendered  probable  that  minute  metallic  admixtures  de- 
tected in  the  country-rock  by  Sandberger's  method  are  really  de- 
rived from  the  ore-deposit,  i.e.,  are  not  idiogenous  but  xenogenous. 
His  assumptions  in  this  field  also  are  thus  shown  to  be  indefensi- 
ble. 

While  I  acknowledge  fully  the  great  importance  of  chemical  data 
for  the  explanation  of  vein-phenomena,  I  cannot  give  here,  without 
becoming  too  prolix,  all  the  chemical  views,  often  quite  discordant, 
and  must  content  myself  with  the  description  of  a  theory  of  ore-de- 
posits based  upon  purely  chemical  grounds,  which  has  just  been 
made  public  by  De  Launay.  The  author  starts  chiefly  from  the 
views  of  Elie  de  Beaumont*  concerning  volcanic  and  metallic  eman- 
ations, adding  to  these  the  results  of  the  studies  of  Fouque,  Senar- 
mont,  Ebelmen,  St.  Claire  Deville,  Daubree,  etc.  He  begins  with 
the  primitive  occurrence  of  magnetite  in  the  eruptive  rocks,  which  he 
extends  to  many  other  metals  and  minerals  whose  primitive  presence 
in  eruptives  has  not  been  demonstrated.  Certain  metallic  substances 
were  segregated  in  cooling  from  the  molten  mass;  others  have  been 
dissolved  from  the  eruptive  rock  in  depth  by  "  mineralizers,"  such 
as  emanations  of  chlorine,  fluorine,  sulphur,  etc.,  and  have  been  de- 
posited in  the  channels  leading  to  the  surface.  De  Launay  is  a  very 
positive  ascensionist ;  he  also  doubts  the  primitive  deposition  of  ores 
in  marine  basins,  and  thus  comes  by  the  path  of  chemical  specula- 
tion to  results  analogous  to  mine.  Volcanic  and  ancient  eruptive 
rocks;  fumaroles  and  mofettes ;  geysers  and  thermal  springs — these 
indicate  the  ways  by  which  the  metals  have  reached  the  earth's  sur- 
face. But  of  such  assumptions  we  must  obtain  assurance  through 
observations  in  other  directions.  Views  based  upon  purely  chemi- 
cal conclusions  are  not  sufficiently  convincing  for  us,  because  they 
are  gained  in  the  chemical  laboratory  under  conditions  different, 
especially  as  to  pressure  and  temperature,  from  those  which  obtain 
in  the  deep  region. 

Manner  of  Filling  of  Open  Spaces  in  General. 

We  know  already  that  cavities,  however  originated,  are  always 
filled  in  analogous  ways.  We  find  in  vein-spaces,  in  the  spaces  of 

*  Elie  de  Beaumont,  Bulletin  de  la  Soc.  geol.  de  France,  2  ser.,  iv.,  p.  1249. 

i 


THE   GENESIS   OF   ORE-DEPOSITS.  59 

dissolution,  and  even  in  individual  geodes  of  opal  and  chalcedony, 
always  the  same  elements  of  structure,  though  in  the  most  widely 
different  materials. 

Considering  the  matter  closely,  we  find  that  many  things  are  pecu- 
liar to  the  shallow  region,  as  the  nearest  to  atmospheric  influences; 
but  some  things  experienced  in  that  region  may  be  used  to  explain 
the  phenomena  of  deposits  in  the  deep  region  also. 

Since  we  have  seen  that  the  precipitate  in  an  approximately  hori- 
zontal pipe,  entirely  filled  with  liquid,  attaches  itself  to  the  whole 
interior  surface,  the  same  must  be  true  for  an  underground  channel, 
and  all  the  more  if  it  approaches  a  vertical  position.  Under  such 
circumstances  the  deposit  or  mineral  crust  will  cover  uniformly  the 
whole  wall-surface. 

Evidently  the  same  laws  govern  here  as  in  sedimentation.  When 
the  section  of  the  passage  through  which  the  liquid  flows  under  a 
given  pressure  is  relatively  small,  the  deposit  will  take  place  only 
when  the  passage  is  enlarged.  This  explains  the  sometimes  unequal 
distribution  of  ore  in  one  and  the  same  mineral-water  channel. 

As  in  a  saturated  solution  a  precipitate  may  be  obtained  upon  any 
solid  body  introduced,  so  in  our  mineral-water  channels  deposits 
will  be  made  upon  all  solid  bodies — splinters  or  masses  of  rock  fallen 
into  the  fissure,  loose  pieces  of  older  mineral  crusts,  and  individual 
crystals  floating  in  the  liquid. 

The  size  of  the  rock-fragments  here  considered  is  very  variable. 
We  might  include,  for  instance,  those  which  are  inclosed  between 
two  regular  vein-branches.  But  we  will  narrow  our  view  to  what 
can  be  seen  from  a  single  standpoint  in  the  mine,  and  then  we  ob- 
serve that  horses  of  several  square  meters'  surface  are  uniformly 
crusted,  like  small  pieces  of  country-rock  found  in  the  vein-filling, 
the  only  difference  being,  perhaps,  that  the  crusts  are  thicker  and 
more  numerous  upon  the  larger  masses.  The  fragments  of  rock, 
either  angular  or  already  more  or  less  rounded,  form,  when  incrusted, 
the  so-called  sphere-,  cocarde-,  or  ring-ores.  Crusted  rock-kernels 
may  often  be  observed  coexisting  with  distinct  wall-crusts.  Some- 
times the  latter  are  less  prominent  than  the  former,  and  the  ore- 
deposit  then  has  the  appearance  of  a  breccia  or  a  conglomerate,  the 
several  fragments  of  which  are  held  together  by  the  mineral  crusts. 
If,  on  the  plane  of  a  given  section,  there  appear  no  points  of  contact 
between  the  fragments,  it  must  not  be  concluded  that  they  originally 
hung  free  in  the  vein-space,  or  that  they  have  been  pressed  apart  at 
a  later  period  by  the  force  of  crystallization  of  the  mineral  crusts, 


60  THE   GENESIS   OF    ORE-DEPOSITS. 

for  the  actual  points  of  contact  can  be  found  in  a  pirallel  section  ; 
at  least,  I  have  always  found  them  when  I  have  sliced  into  plates  a 
specimen  on  the  surface  of  which  they  were  not  shown.  I  mention 
this  circumstance  because  many  extensive  discussions  have  been  based 
upon  imperfect  views  of  single  sections,  giving  deceptive  indications 
of  structure.* 

I  would  recommend  the  frequent  preparation  of  sections  and  slides 
of  such  apparently  complicated  structures,  and  I  am  convinced  that 
seeming  contradictions  and  difficulties  would  be  simply  explained 
thereby.  It  is  only  a  question  of  correct  observation  and  represen- 
tation, for  which,  it  must  be  confessed,  the  use  of  coloring  may  be 
necessary.  In  this  connection  I  must  remark  that  illustrations,  er- 
roneous in  this  respect,  have  found  their  way  even  into  text-books, 
as,  for  instance,  the  picture  of  cocarde-ore  given  by  Cotta,f  which  is 
taken  from  a  careful  but  uncolored  drawing  by  Weissenbach,J  of 
which  I  reproduce  a  part  in  Fig.  17.  Fragments  of  mica-slate  are 
crusted  with  layers  of  quartz  and  pyrite,  and  in  the  vugs  there  is 
sometimes  also  manganese  or  brown-spar.  The  radial  appearance 
of  the  crusts  in  the  drawing  is  evidently  due  to  the  position  of  the 
crystals  perpendicular  to  the  wall -surfaces,  and  is,  as  a  rule,  observ- 
able in  all  such  cases.  The  same  figure  from  Weissenbach  has  been 
used  by  A.  Daubree  also§,  as  an  instance  of  a  filon  br&cheform;  but 
the  several  crusted  rock- fragments  are  separated  by  heavy  lines, 
which  make  the  representation  not  only  incorrect  but  incomprehen- 
sible. 

The  phenomenon  may  be  most  generally  illustrated  by  Fig.  18, 
which  represents  a  section  through  a  gold-specimen  from  the  Ka- 
trontza  ore-body  at  Verespatak,  and  of  which  I  intend  to  publish 
in  my  monograph  on  the  occurrence  of  gold  in  Transylvania  a  series 
of  parallel  sections  in  color.  Four  pebbles,  three  of  quartz-porphyry 
and  one  of  mica-slate,  are  regularly  crusted  with  (1)  a  thin  zone 
of  hornstone,  (2)  a  thin  crust  of  pyrite,  composed  of  several  layers  no 
thicker  than  paper,  (3)  hornstone,  in  which  occurs  (4)  a  zone,  5  mm. 
(0.2  in.)  in  average  thickness,  of  fine  aggregates  of  native  gold,  ex- 
tending often  into  the  next  following  crust  (5)  of  quartz,  containing 

*  E.g.,  Tram.  A.  I.  M.  E.,  1883,  xi ,  119. 

f  Lehre  von  den  Erzlagerstalten,  Part  I.,  Freiberg,  1859,  p.  33. 

J  G.  G.  A.  von  Weissenbach.  Abbilduny  merkwurdiger  Gangverhaltnisse.  Leip- 
zig. 1836,  Fig.  2. 

g  A.  Daubre'e.  Les  eaux  souterraines  aux  epoques  anciennes.  Paris,  1887,  Fig.  24, 
p.  64. 


THE   GENESIS   OF   ORE-DEPOSITS.  61 

scattered  clouds  of  hornstone.  The  series  ends  in  this  specimen  (6) 
with  open  central  druses.  But  other  specimens  from  the  same  de- 
posit show  also  minute  crusts  of  manganese- spar,  to  which  I  shall 
recur. 

Fig.  11,  representing  the  occurrence  of  cinnabar  in  the  deeper  work- 
ings at  Sulphur  Bank,  is  an  interpretation  of  the  description  and 
sketch  given  by  Le  Conte  (op.  cit.,  p.  28).  Fragments  of  sandstone 
and  slate  with  somewhat  rounded  edges  are  regularly  surrounded 
with  crusts  of  cinnabar  which  fill  the  space  between,  up  to  the  central 
druse.  Sometimes  crusts  of  hydrated  silica  and  pyrite  appear  also. 
Fig.  10  is  a  picture  of  a  rich  portion  of  the  surface-workings  of 
1874,  which  I  sketched  at  that  time  in  my  note-book.  The  basaltic 
country-rock  is  thoroughly  cut  up  by  irregular  seams,  which  have 
disintegrated  it  to  a  shaly  mass.  In  the  seams,  especially  where 
they  come  together,  larger  spaces  have  been  formed,  often  filled  with 
decomposed  country-rock,  often  showing  separate  crusts  of  cinnabar 
and  opal,  with  a  central  druse.  The  porous  material  of  rock  and 
filling  is  impregnated  with  native  sulphur. 

Fig.  19  shows  the  filling  of  a  space  of  dissolution  at  Raibl.  It  is 
a  diagram  from  the  accurate  picture  in  my  monograph  upon  the  de- 
posit.* A  nucleus  of  limestone  is  surrounded  by  innumerable  fine 
crusts  of  wurtzite  and  more  compact  but  less  regular  layers  of  galena. 

Fragments  of  earlier  mineral  crusts,  which  have  been  in  some 
way  separated  from  their  original  position,  are  often  found  sur- 
rounded by  mineral  crusts  of  later  origin.  An  example  is  shown  in 
Fig.  20,  representing  boiler-scale  from  one  of  the  Przibram  pump- 
ing plants.  Here  fragments  of  dislocated  scale,  about  2  mm.  (0.08 
inch)  in  diameter,  are  enveloped  in  later,  thin  crusts,  and  thus  united 
to  a  breccia.  The  mass  consists  chiefly  of  fibrous  gypsum,  the  fibers 
of  which  stand  perpendicular  to  the  surfaces  to  which  they  are  at- 
tached. 

Figs.  21  and  22  present  a  very  distinct  example,  in  which  earlier 
mineral  crusts,  together  with  adhering  pieces  of  country-rock,  are  sur- 
rounded by  recent  crusts.  These  figures  are  taken  from  the  valuable 
treatise  of  I.  Ch.  Schmidt,f  and  refer  to  Zellerfeld  in  the  Harz, 


*  "  Die  Blei-und  Galmei-Lagerstatten   von  Kaibl  in  Karnthen." — Jahrb.  d.  k.  k. 
geol.  R.  Anstalt,  xxiii.,  1873,  Bd.  I.,  Fig.  13. 

f  I.  Christian  Lebrecht  Schmidt. — Beitrdge  zu  der  Lehre  von  den   Gangen,  Sie- 
gen,  1827. 


62  THE   GENESIS   OF   ORE-DEPOSITS. 

whence  A.  von  Groddeck  also  has  obtained  very  interesting  illustra- 
tions of  vein-filling.* 

I  have  seen  a  more  complicated  example  from  the  Katrontza 
ore-body  at  Verespatak,  where  very  rough  ancient  crusts  of  black 
hornstone  and  parti-colored  quartz  have  been  cemented  together  by 
deposits  of  later  quartz  and  manganese  spar  to  a  compact  mass,  with 
some  central  druses.  Similar  conditions  will  be  seen  to  obtain  in 
the  so-called  pipe-ores  of  Raibl,  Figs.  25  to  28. 

The  variable  relation  between  the  diameter  of  the  nucleus  and 
the  thickness  of  the  surrounding  crust  naturally  contributes  greatly 
to  the  variety  of  the  resulting  appearances.  In  the  pisolitic  forma- 
tion, for  instance,  the  crust  is  many  times  thicker  than  the  nucleus. 

In  some  cases  the  kernels  are  individual  crystals.  I.  Ch.  L. 
Schmidt  describes  pisolitic  forms  from  Warstein,  in  Westphalia,  the 
kernel  of  which  is  a  crystal  of  yellow  eisenkiesel,  about  5  mm. 
(0.2  inch)  in  diameter,  showing  prismatic  and  dihexahedric  faces,  and 
covered  first  with  a  thin,  white  coating,  upon  which  are  crusts  of 
coarsely  fibrous  eisenkiesel.  The  edges  of  these  are  gradually 
rounded,  until  egg-shaped  spheroids,  about  12  mm.  (0.5  in.)  in  di- 
ameter, are  formed,  touching  each  other  at  single  points,  and  leaving 
interspaces,  which  are  either  filled  entirely  with  granular  eisenkiesel, 
or  contain  residual  vugs  lined  with  transparent,  finely  crystalline 
quartz. 

Fig.  24  represents  the  geologically  important  occurrence  of  crusted 
kernels  of  native  gold  from  the  Matyas  Kiraly  mine  at  Verespatak. 
Minute  aggregates  of  native  gold  are  systematically  surrounded  by 
distinct,  beautifully  pink  to  carmine,  thin  crusts  of  rhodonite  or 
rhodochrosite.  So  long  as  the  kernels  were  completely  separated,  or 
were  kept  suspended  by  the  disturbance  traversing  the  cavity,  these 
crusts  were  deposited  entirely  around  each.  After  they  had  become 
fixed,  later  deposits  of  the  same  sort  covered  them  ;  then  followed 
carbonates  of  lime  and  iron ;  and  finally  came  the  quartz,  the  beau- 
tiful water-clear  crystal-tips  of  which  project  into  the  central  druses. 

The  occurrence  of  gold  in  manganese  spar  is  not  rare  at  Veres- 
patak ;  ornaments  cut  from  this  material  are  pretty  widely  sold. 
But  I  have  found  but  once  such  a  distinct  envelopment  of  the  gold 
by  the  rhodochrosite  crusts.  The  figure  represents  a  piece  cut  for  a 
brooch,  which  is  in  my  wife's  possession.  It  is  specially  interesting, 
also,  as  showing  that  the  gold  was  not  derived  from  the  secondary 

*  A.  von  Groddeck.—  Ueber  die  Erzgdnge  des  Oberharzes.  (Inaugural  dissertation) 
Berlin,  1867. 


THE   GENESIS   OF   OKE-DEPOSITS.  63 

decomposition  of  auriferous  sulphides  or  tellu rides  in  loco,  but  was 
directly  precipitated  from  the  mineral  solutions  which  subsequently 
deposited  the  surrounding  crusts. 

We  have  seen  that  within  the  domain  of  vadose  or  shallow  cir- 
culation peculiar  deposits,  classed  as  stalactites,  are  very  common,  not 
only  in  the  spaces  eroded  by  the  natural  circulation  of  the  ground- 
water,  but  also  in  spaces  created  through  the  artificial  depression  of 
the  water-level  by  mining.  In  the  latter  case,  since  mining  often 
follows  ore-deposits  into  the  deep  region,  a  much  larger  variety  of 
substances  is  exposed  to  alteration,  so  that  stalactitic  formations  of  all 
kinds  of  materials  may  be  encountered.  Chiefly,  however,  we  find 
in  this  form  the  results  of  oxidation,  and  it  is  somewhat  exceptional 
to  meet  with  the  products  of  reduction,  effected  by  organic  matter 
in  the  mine.  The  most  frequent  of  these  are  stalactites  of  pyrite. 

This  circumstance  led  to  the  opinion  that  stalactites  in  an  ore- 
deposit  should  be  taken  as  characteristic  of  a  vadose  or  shallow 
origin,  through  the  descending  movement  of  the  solutions  which 
formed  the  stalactites.  This  view  has  been  most  clearly  advanced 
by  Dr.  A.  Schmidt.*  The  earliest  formations  in  the  instructive 
Wiesloch  deposits  are  the  sulphides,  marcasite,  galena  and  wurtzite, 
to  the  decomposition  of  the  latter  of  which,  through  the  metaso- 
matic  replacement  of  the  carbonate  of  lime  by  the  carbonate  of  zinc, 
the  zinc-ore  deposits  are  due.  These  he  held  to  be  clearly  vadose  in 
origin ;  and  since  the  sulphides  also  occur  in  stalactites,  he  concluded 
that  they  likewise  must  have  been  formed  by  infiltration  from  above. 
The  fact  that  these  latter  formations  now  lie  below  water-level, 
whereas  the  formation  of  stalactites  requires  a  space  filled  with  air 
or  gas,  only  forced  him  to  endeavor  to  explain  this  contradiction  by 
the  hypothesis  of  suitable  elevations  and  depressions  either  of  the 
water-level  or  of  the  land  itself. 

But  all  this  would  have  been  unnecessary  if  he  had  borne  in 
mind  that  ascending  liquids  under  a  certain  pressure  will  penetrate 
into  a  cavity  from  all  sides,  and  may  enter  through  the  roof  if  the 
bottom  and  walls  are  less  permeable.  He  distinguishes  in  general 
two  forms  of  development  in  the  original  ore-deposition,  namely,  the 
filling  of  the  lower  part  of  a  cavity  with  nearly  horizontal,  undu- 
lating crusts  of  wurtzite,  with  a  little  galena,  and  the  stalactites  which 
hang  from  the  roof,  there  being  no  discoverable  trace  of  correspond- 
ing stalagmites  below.  This  indicates  that  the  cavity  was  not 

*  Die  Zinkerzlagerstatten  von  Wiesloch  in  Baden,  Heidelberg,  1881,  p.  94. 


64  THE   GENESIS   OF   ORE-DEPOSITS. 

wholly  filled  with  gas,  but  only  in  its  upper  part,  to  which,  conse- 
quently, the  stalactitic  forms  are  confined.  As  to  the  manner  of  the 
later  decomposition  of  the  wurtzite,  which  extends  down  to  the 
present  water-level,  there  can  be  no  doubt  (op.  cit.,  p.  101). 

Similar  conditions  are  found  in  Raibl,  where  I  have  carefully 
studied  the  stalactites  locally  called  "pipe-ores."*  I  find  these,  it 
is  true,  not  in  their  original  position  at  the  roof  of  the  cavities,  but 
in  the  midst  of  the  filling,  already  broken  off  and  surrounded  by 
the  latest  mineral  crust,  in  a  dolomite  spar.  They  seem  to  have 
occurred  at  many  points  in  this  deposit,  but  my  observations  were 
confined  to  two,  one  of  which  was  on  the  5th  Johanni  level,  about 
400  meters  (1312  feet)  above  the  deepest  adit  (the  bottom  of  the 
valley),  while  the  other  was  on  the  7th  deep  level,  about  60  meters 
(196  feet)  below  the  said  adit.  The  former  of  these  two  points  was 
within  the  influence  of  the  ground-water. 

Under  the  conditions,  decomposition  of  pyrite  and  zinc-blende 
had  been  specially  great ;  that  of  galena  less  so.  It  was  often  pos- 
sible to  extract  from  the  dolomite  mass  the  stems  of  galena  which 
were  loose  in  it.  The  axis  of  such  a  stalactite-stem  (frequently  over 
10  centimeters — 4  inches — long)  was  often  an  open  space  through 
which  one  could  blow  air,  whence  the  name  "pipe-ore"  given  to 
this  surprising  occurrence.  Specimens  not  decomposed  or  in  early 
stages  of  alteration  showed,  besides  galena,  crusts  of  pyrite  and 
zinc-blende,  concentrically  disposed  around  the  axis. 

Figs.  25,  26,  27  and  28  (taken  from  my  former  treatise)  and  rep- 
resenting sections  of  individual  stalactites,  are  intended  to  cover  the 
variety  of  forms  in  these  occurrences.  Fig.  25  shows  a  circular 
stalactite  in  which  small  quantities  of  galena  may  be  seen  in  the  py- 
rite surrounding  the  axial  cavity.  The  outer  crust  consists  of  thin 
layers  of  wurtzite  (Schalenblende).  In  Fig.  27  a  galena  mass  of 
rhombic  section,  with  regular  striations  of  secretion,  sits  imme- 
diately on  the  side  of  the  cavity.  In  Fig.  26  the  annular  mass  of 
galena  is  surrounded  by  blende.  In  Fig.  28  a  decomposed  body  of 
blende  lies  within  the  galena  mass,  which  latter  is  deposited  imme- 
diately in  the  granular  dolomite.  It  will  be  seen  that  the  crusts 
upon  the  stalactites  present  a  varying  order  of  succession,  and 
that  the  stalactites  have  fallen  from  the  roof  at  different  stages  of 
their  growth. 

*  F.  Posepny,  "  Die  Blei-und  Galmci-Erzlagerstatten  von  Raibl."  Jahrb.  d.  k.  k. 
(jeol.y  R.  A.,  xviii.,  1873,  p.  372;  also  "  Ue.ber  die  Rohrenerze  von  Raibl,"  Verhandl, 
d.  k.  k.  g.  R.  A.t  1873,  p.  54. 


THE   GENESIS   OF   ORE-DEPOSITS.  65 

That  portion  of  the  ore-deposit  which  surrounds  the  localities  of 
these  stalactites  has  an  entirely  normal  structure,  corresponding  with 
that  of  other  portions,  and  can  only  have  been  formed  in  the  same 
way,  namely,  from  ascending  mineral  solutions  in  the  deep  region 
When,  under  such  circumstances,  a  cavity  contains  stalactitic  de- 
posits instead  of  the  ordinary  wall-deposits,  that  particular  part  of 
the  channel  must  have  been  filled  with  gas.  The  decomposition  of 
the  blende  is  due  here,  as  in  Wiesloch,  to  the  subsequent  action  of 
the  vadose  circulation. 

In  the  Matyas  Kiraly  mine  in  Verespatak,  from  which  I  have 
already  described  the  envelopment  of  gold-aggregates  by  various 
metallic  carbonates  and  quartz,  there  has  been  found  also  a  stalac- 
titic form  of  analogous  composition.  This  specimen  is  in  my  pos- 
session, but  there  are  two  others  in  the  National  Museum  at  Buda- 
pest which  practically  came  from  the  same  mine.  One  of  the  latter 
is  shown  in  Figs.  29  and  30,  and  my  own  in  Fig.  31,  in  twice  the 
natural  size.  The  latter  showed,  after  being  broken  from  the  rock 
in  which  it  occurred,  a  projecting  thread  of  gold;  and  in  polishing 
the  surface  several  angular  (and  hence  crystalline)  gold-aggregates 
were  found  in  the  axis  of  the  stalactite.  The  shaded  portion  indi- 
cates the  pink  manganese  crusts,  and  the  unshaded  portion  the  color- 
less carbonates.  The  outermost  crust,  separated  here  and  there  from 
the  others  by  a  small  druse,  is  quartz. 

Wonderful  occurrences  of  this  kind  must  exist  in  the  Valle  mines 
in  Missouri;  but  we  have  only  mere  diagrams  of  them,  which  do 
not  exhibit  the  true  details  and  cannot  be  corrected  with  the  aid  of 
the  accompanying  text.  The  careful  objective  representation  of  a 
series  of  these  tubular  deposits  would  be  a  service  to  science.  I 
shall  recur  to  these  relations,  represented  in  Figs.  32  to  35,  when  I 
come  to  consider  the  Missouri  deposits  again. 

The  variety  of  the  occurrences  described  above  might  be  still 
further  illustrated ;  but  enough  has  been  said  to  furnish  from 
observation  the  elements  for  explaining  the  filling  of  all  crustified 
deposits.  When  the  elements  actually  found  in  such  deposits  are 
taken  together  with  what  we  know  of  the  conditions  of  under- 
ground circulation,  no  competent  person  can  well  believe  in  any 
other  origin  for  these  deposits  than  that  of  the  circulation  we  have 
described.  Whoever  has  followed  the  foregoing  simple  statement 
of  the  whole  chain  of  phenomena  will  be  led  to  distinguish  sharply 
between  the  effects  of  the  descending  vadose  and  those  of  the 
ascending  profound  circulation,  and  to  avoid  the  confusion  of 

5 


66  THE   GENESIS   OF   ORE-DEPOSITS. 

the  two  which  sometimes  characterizes  the  discussion  of  the 
subject. 

But  there  remains  a  serious  difficulty  in  determining  the  genesis 
of  non-erustified  deposits.  Here  the  indications,  by  which  the 
structure  and  gradual  growth  of  the  deposit  may  be  traced,  are  at 
first  Jacking.  But  they  will  certainly  be  found  by  patient  search  ; 
and  this  knowledge  must  be  furnished  by  engineers  who  have 
opportunity  to  study  the  phenomena  on  the  spot  where  they  occur, 
namely,  in  the  mine. 

The  non-crustified  deposits  consist,  however,  of  the  same  min- 
erals as  the  crustified,  and  cannot  well  have  a  different  origin ;  only 
we  are  not  yet  in  a  position  to  offer  for  them  similar  proofs  of  the 
manner  of  their  formation.  Certainly  they  also  are  the  products 
of  ascending  mineral  solutions ;  but  they  were  not  deposited  in 
pre-existing  spaces,  and  consequently  they  show  no  crustification. 
In  describing  various  instances  of  this  class,  I  shall  have  occasion 
to  adduce  some  data  bearing  upon  their  genetic  relations. 

But  even  the  crustified  deposits  need  to  be  further  illustrated  by 
examples,  especially  because  they  seldom  occur  in  nature  in  pure, 
unmixed  types.  We  ought  not  to  consider  ore-deposits  without 
reference  to  the  medium  which  contains  them;  hence  we  must  take 
into  consideration  the  country-rock,  and  seek  to  represent  the  analo- 
gies of  nature  by  grouping  them  graphically,  as  it  were,  with  rela- 
tion to  two  axes,  representing  respectively  the  genetic  class  and  the 
country-rock.  We  may  thus  distinguish  the  following  general 
groups : 

Fillings  of  spaces  of  discission  (fissures,  etc.). 

Fillings  of  spaces  of  dissolution  in  soluble  rocks. 

Metamorphic  deposits  in  soluble  rocks;  in  simple  sediments  ;  in 
crystallines  and  eruptives. 

Hysteromorphous  deposits  (secondary  deposits,  due  to  surface 
agencies). 

PART  II. 
EXAMPLES  OF  CLASSES  OF  DEPOSITS. 

I  have  attempted  to  show  above  that  in  the  two  regions  of  sub- 
terraneous circulation  the  formation  of  ore-deposits  must  have  taken 
place  according  to  different,  almost  diametrically  opposed  principles  : 
in  the  vadose  region  through  descension  and  lateral  secretion,  and 
in  the  profound  region  by  ascension,  as  the  product  of  upward  cur- 


THE   GENESIS   OF   ORE-DEPOSITS.  67 

rents.  I  have  pointed  out  that  the  deepest  rocks  reached  by  mining 
can  scarcely  be  the  original  sources  of  the  metallic  solutions,  and 
that  these  sources  must  lie  at  still  greater  depths. 

That  is  to  say,  I  advocate  the  views  of  the  old  school,  and  stand 
opposed  to  the  assumptions  of  the  new  one,  lately  become  popular, 
which  does  not  need  to  go  to  inaccessible  depths  for  the  source  of 
the  metals,  but  professes  to  find  it  conveniently  by  simple  chemical 
tests,  without  the  necessity  of  leaving  the  laboratory  and  searching 
out  the  natural  deposits.  The  new  doctrine  has  thus  far  failed  to 
take  into  consideration  the  two  different  underground  regions;  and 
we  may  expect  that  in  proportion  as  it  comes  to  do  so,  its  conclu- 
sions will  acquire  quite  another  meaning. 

I  think  it  has  been  shown  that  the  deposits  of  the  deep  region 
are  precipitates  from  ascending  springs.  It  remains  to  inquire,  what 
has  become  of  the  substances  which  were  not  precipitated  in  such 
channels,  but  reached  the  surface  in  solution?  Evidently  these 
have  been  taken  up,  partly  by  the  surface  circulation,  partly  by  the 
vadose  underground  currents ;  and,  in  the  latter  case,  the  deposition 
of  such  substances  in  the  vadose  region  is  possible.  But  I  do  not 
believe  that  we  are  as  yet  in  a  position  to  form  a  correct  conception 
of  the  process  of  such  a  deposition;  and  therefore  I  leave  this 
question  open.  Possibly,  many  impregnations,  for  which  we  can 
trace  no  direct  connection  with  ascending  springs,  yet  which  are 
certainly  not  idiogenous  (i.e.9  of  contemporaneous  origin  with  the 
rock-matrix),  may  have  originated  in  this  way.  Possibly,  the  sul- 
phides which  occur  confined  to  the  neighborhood  of  organic  remains 
have  been  reduced  from  sulphates.  But  this  must  be  confirmed  in 
each  case  by  a  direct  study  of  the  facts,  and  not  propounded  as  a 
safe  generalization  for  all  cases. 

All  these  conclusions  are  based  upon  the  undoubtedly  correct 
hypothesis  that  the  individual  minerals  of  the  deposits  are  precipi- 
tates from  aqueous  solutions.  The  important  part  played  by  the 
direct  products  of  the  barysphere — the  eruptive  rocks — is  not  ig- 
nored. But  there  has  been  a  tendency  of  late  to  consider  the  proof 
of  any  solvents  as  superfluous,  and  apparently  to  assume  that  cer- 
tain minerals  were  segregated  directly  from  the  eruptive  magma. 
With  respect  to  ferriferous  oxides,  this  view  has  some  foundation  ; 
but  the  notion,  apparently  held  in  some  quarters,  that  sulphides 
also  were  thus  segregated  from  the  magma,  surpasses  my  compre- 
hension. It  is  true  that  pyrite  is  sometimes  seen  upon  the  lavas  of 
active  volcanoes ;  but  this  occurs,  so  far  as  I  know,  only  when  fuma- 


(58  THE   GENESIS   OF   ORE-DEPOSITS. 

roles  and  solfataras  emit  gases  and  vapors  which  decompose  the 
rock,  and  therefore  the  agency  of  a  solvent  is  not  lacking.  I  am 
therefore  obliged  to  conclude  that  aqueous  solvents  are  the  chief  factor 
in  the  genesis  of  ore-deposits ;  and  I  shall  be  guided  by  this  princi- 
ple in  the  following  illustrations  of  the  leading  genetic  groups. 

1.  ORE- DEPOSITS  IN  SPACES  OF  DISCISSION. 

The  spaces  produced  in  rocks  by  mechanical  forces  are  predomi- 
nantly fissures;  but  simple  forms  are  sometimes  rendered  irregular 
by  pre-existing  conditions,  such  as  those  of  stratification.  Splitting 
upon  a  bedding-plane,  coupled  with  a  simultaneous  longitudinal 
movement  (such  as  gave  rise  to  the  ore-stock-works  which  the 
Norwegian  miners  call  "  lineal  ")  may  produce  very  complicated 
spaces,  which  must,  however,  be  classed  as  spaces  of  discission. 

Every  fissure  is  the  consequence  of  a  tendency  to  dislocation 
transmitted  into  the  rock.  Hence  the  principal  effect  of  the  process 
is  the  production  of  the  dislocation,  not  that  of  the  fissure.*  Where 
yielding  stratified  rocks  are  exposed  to  such  a  force,  they  first  bend 
in  its  direction,  and  the  fracture  takes  place  when  the  limit  of 
elasticity  i*  passed.  In  such  cases  it  is  evident  that  the  movement 
precedes  the  fracture.  Fig.  70,  from  Rodna,  and  Fig.  69,  from 
Raibl,  are  examples.  In  the  latter,  the  gently  southward-dipping 
contact  between  limestone  and  slate  is  bent  and  faulted  by  a  N.  and 
8.  fissure.  At  Kisbanya,  in  Transylvania  (Fig.  99),  the  strata  of 
gneiss  and  chloride  slate,  striking  N.  and  S.,  are  so  bent  by  the  E. 
and  W.  Nagynyerges  vein  as  to  give  the  appearance  of  an  ore- 
bed. 

Although  the  fissures  produced  by  dislocating  forces  appear  to  be 
straight,  they  exhibit  (as  may  be  observed  where  veins  have  been 
traced  for  long  distances)  various  changes  of  direction  and  more  or 
less  gradual  curves.  This  hinders  or  checks  the  movement  of  one 
convex  portion  upon  another,  and  promotes  the  creation  of  open 
spaces.  The  dislocating  force,  however,  continually  crowds  the 
projecting  surfaces  together,  and  thus  a  space  already  partly  filled 
with  mineral  deposit  may  be  closed,  or  an  open  space  may  be  filled 
with  the  detritus  of  friction.  But  the  space  finally  left  open 
facilitates  communication  with  the  deep  region,  from  which  it  is 
filled. 

*  F.  Posepny,  "  Geol.  Betracht.  ttber  die  Gangspalten,"  Jahrb.  d.  k.  k.  Beryakade- 
mt'en,  Vienna,  1874. 


THE   GENESIS   OF   ORE-DEPOSITS.  69 

According  to  this  conception,  the  vein-sheet  must  not  be  regarded 
(as  is  too  often  done)  as  a  uniform  plate  of  ore.  On  the  contrary,  it 
consists  of  several  portions  of  very  unequal  value.  The  most 
valuable,  doubtless,  is  the  cavity-filling  which  forms  the  bonanza 
proper.  In  another  portion  the  mineral  solutions  have  been  forced 
to  penetrate  the  country-rock,  and  impregnate  it  with  ore.  A  third 
portion  remained  altogether  impenetrable  to  the  solutions,  and  repre- 
sents barren  ground.  These  three  kinds  of  ground  may  evidently 
show,  at  least  in  the  same  district,  a  certain  regularity  of  relation  ; 
and  of  course  it  is  most  important  to  determine  for  a  given  district 
some  law  of  distribution  of  the  rich  ore-bodies.  In  certain  instances 
some  knowledge  of  this  distribution  has  been,  in  fact,  successfully 
acquired  for  a  given  vein,  before  it  had  been  exhausted  by  mining. 
In  many  other  cases  we  cannot  establish  the  law,  even  afterwards, 
because  the  most  necessary  records  were  not  made  during  the  ex- 
ploitation. On  the  whole,  we  must  confess  that  our  knowledge  of 
the  laws  of  bonanzas  is  nothing  to  be  proud  of.  In  this  respect  the 
work  of  Professor  Moissenet  may  be  consulted.* 

Obviously,  in  all  such  investigations,  the  question  of  the  origin  of 
the  fissure  must  be  separated  from  that  of  its  filling.  The  former  can 
be  answered  only  upon  the  broad  basis  of  a  knowledge  of  the 
stratigraphic  relations  of  the  whole  vicinity,  and  with  reference 
chiefly  to  the  physical  properties  of  the  rocks,  while  in  the  latter 
their  chemical  properties  come  to  the  front. 

As  a  rule,  however,  the  country-rock  of  an  ore- vein  is  more  or 
less  altered,  not  only  by  decomposition,  but  also  by  subsequent 
solidification,  thus  rendering  much  more  difficult  the  comparison 
with  conditions  existing  far  from  the  vein.  This  alteration  of  the 
country-rock  is  universally  ascribed  to  the  mineral  solutions  which 
deposited  the  ore;  and  it  is  not  improbable  that  a  close  study  of  it 
might  enable  us  to  draw  conclusions  as  to  the  nature  of  these  solu- 
tions. Unfortunately,  petrography  is  still  confined  mainly  to  fresh, 
typical  rocks,  and  the  study  of  the  decomposed  country-rock  of  ore- 
veins  has  not  been  cultivated  so  much  as  could  be  wished. 

All  veins  which  exhibit  friction-phenomena,  such  as  crushed 
country-rock,  slickensides,  and  striations,  are  structurally  fault- 
fissures.  Such  a  vein  may  be  conceived,  therefore,  as  the  boundary- 
surface  of  a  mass  which  has  undergone  movement.  The  vein- 
phenomena  of  the  Hartz  especially  support  this  conception. 

*  M.  L.  Moissenet,  Etudes  sur  Us  filons  de  Cornwall ;  Parties  riches  des  filons ; 
Structure  de  ces  parties,  etc.,  Paris,  1874.  Engl.  tr.  by  J.  H.  Collins,  London,  1877. 


70  THE   GENESIS   OF   ORE-DEPOSITS. 

Some  vein-fissures  are  confined  to  a  given  rock,  and  do  not  ex- 
tend into  the  adjacent  rock.  These  cannot  be  ascribed  to  struc- 
tural dislocation,  but  must  rather  be  considered  as  caused  by 
changes  of  volume  in  the  immediate  formation.  They  are  often 
called  fissures  of  contraction.  The  most  striking  example  which 
I  have  encountered  is  shown  in  Fig.  36,  which  is  from  the  gold- 
district  of  Beresov,  in  the  Ural  mountains.  Palaeozoic  slates  are 
there  traversed  by  a  number  of  granite  veins,  20  to  40  meters 
(66  to  131  feet)  thick,  and  striking  chiefly  N.  and  S. ;  and  each 
of  these  granite  veins  is  again  traversed  by  E.  and  W.  gold-quartz 
veins,  which  at  the  borders  of  the  granite  either  become  barren  or 
cease  altogether.  Near  the  Beresov  is  the  Pysminsk  district,  in 
which  the  granite  veins  are  replaced  by  diorite  and  serpentine  ;  but 
strange  to  say,  the  gold-quartz  veins  occupy  in  these  rocks  the  same 
position  as  in  the  peculiar  Beresov  granite,  locally  called  beresite. 
Judging  from  Beresov  alone,  one  might  suspect  the  veins  to  have 
been  filled  from  the  granite;  but  the  occurrence  in  Pysminsk  sug- 
gests caution. 

Finally,  the  veins  of  the  well-known  very  deep  mines  of  Przibram 
might  be  ascribed  to  the  contraction  of  the  eruptive  dikes  in  which 
they  occur  (although  they  depart  here  and  there  into  the  stratified 
rocks) ;  but  we  cannot  dream  of  deriving  their  metallic  filling  from 
the  dikes.  The  Commission,  already  mentioned,  established  to  test 
the  applicability  of  the  lateral-secretion  theory  to  Przibram  condi- 
tions, found  the  material  of  the  dikes  to  be  the  same  in  depth  as  in 
the  upper  zones.  The  largest  amount  of  metallic  contents  attributed 
to  the  diorite  dikes  would  account  for  a  portion  only  of  the  thick- 
ness of  ore  in  the  veins.  The  greater  part  must  certainly  be  regarded 
as  of  deep  origin ;  and  it  is  more  convenient  to  treat  the  entire 
metallic  contents  of  the  veins  as  derived  from  greater  depths. 

Granting,  then,  that  the  vein-spaces  at  Beresov  were  formed  by 
the  contraction  of  the  granite  dikes,  the  vein-filling  must  be  ascribed, 
like  that  of  other  deposits,  to  metallic  solutions  ascending  from  the 
deep  region. 

With  regard  to  structure,  the  fillings  of  ore- veins  very  often 
exhibit  distinct  crustification,  and  sometimes  even  a  symmetric  suc- 
cession of  crusts  from  both  walls  to  the  central  druse.  But  this 
phenomenon  often  retires  into  the  background ;  crustification  be- 
comes indistinct  or  disappears,  as  is  frequently  the  case  in  gold- 
quartz  and  other  metamorphosed  veins,  in  which  its  last  traces 
appear  in  the  crystal-tips  of  the  central  druse  and  the  occasional 
indication  of  fibers  perpendicular  to  the  walls. 


THE   GENESIS   OF   ORE-DEPOSITS.  71 

Sometimes  one  part  of  a  vein  shows  distinctly  a  cruslification 
which  in  other  parts  is  discerned  with  difficulty,  or  is  even  wholly 
absent.  Fig.  53  represents  a  specimen  from  the  Drei  Prinzen  Spat 
vein  in  the  eighth  level  of  the  Chnrprinz  Friedrich  August  mine  at 
Freiberg.  It  is  interesting  also  by  reason  of  the  two  dislocations 
which  it  exhibits.  The  oldest  vein  (a)  of  quartz,  with  irregularly 
disseminated  galena  and  zinc-blende,  is  traversed  and  faulted  by  a 
second,  very  clearly  crustified,  vein,  the  filling  of  which  consists  of 
hundreds  of  very  thin  alternate  crusts  of  (6)  fluorite  and  quartz  and 
(c)  barite,  symmetrically  arranged  on  both  sides,  with  a  central 
druse  (d)  containing  a  gray  earthy  mass.  A  quartz  seam  (e  /)  then 
faults  both  veins.  The  manager  of  the  mine  assured  me  that  the 
specimen  occurred  in  the  vertical  position  in  which  I  sketched  it. 
(In  order  to  be  certain  at  all  times  on  this  important  point,  it  is 
advisable,  before  removing  a  specimen  from  its  natural  position,  to 
mark  it  in  color  with  a  vertical  arrow,  head  downward.) 

Very  often  the  crustification  of  a  vein-formed  ore-deposit  is  only 
to  be  traced  in  the  appearance  of  the  whole,  since  each  of  many  ir- 
regular veinlets  may  represent  separate  mineral  crusts.  Accurate 
pictures  of  such  occurrences  are  highly  instructive,  since  the  com- 
plications are  often  so  great  that  the  most  detailed  description  can 
convey  no  correct  notion.  Figs.  45  to  52,  by  reason  of  their  small 
scale,  do  not  give  all  the  details  contained  in  the  originals  from 
which  they  are  taken.  Figs.  45,  46,  and  47  are  from  Weisenbach's 
famous  book,*  and  represent  Freiberg  occurrences.  The  rest  are 
from  Austrian  publications.f  Figs.  48, 49,  and  50  refer  to  Przibram, 
Figs.  51  and  52  to  Joachimsthal.  We  have  in  Fig.  47  a  speci- 
men, so  to  speak,  of  the  transition  from  a  vein  to  a  bedded  de- 
posit. But  this  is  not  the  type  called  by  the  Germans  bed-vein 
(Lagergang),  which  is  strictly  a  fissure-vein,  the  fissure  of  which 
coincides  with  the  plane  of  stratification  instead  of  crossing  it. 
Sometimes  it  is  a  joint  or  cleavage-plane  (often  confounded  with  the 
bedding)  which  the  bed-vein  occupies — a  case  which,  I  believe,  I 
have  found  at  Mitterberg  in  Salzburg  and  at  the  Rammelsberg  near 
Goslar. 

In  this  category  belong  also  the  instances  of  a  squeezing  of  strata 


*  AbbUdung  merkw.  Gangverhaltn.  cms  d.  sacks.  Erzgebirge,  Leipzig,  1836. 

f  Auf  Befehl  s.  Exc>  Julius  Graf  en  Falkenhayn  herausgegebene  Bilder  v.  d.  Lagerst. 
d.  Silber-u.  Bleibergb.  zu  Przibram,  etc.,  Vienna,  1887.  Geol.-bergmdnn.  Karte  mil 
ProfiLen  u.  Ortsbildern  zu  Joachimsthal,  etc.,  Vienna,  1891. 


72  THE   GENESIS   OF   ORE-DEPOSITS. 

near  the  vein,  so  that  hanging  or  foot-wall,  or  both,  show  for  a  cer- 
tain distance  a  stratification  parallel  with  the  ore-deposit,  and  only 
beyond  this  zone  does  the  normal  stratification  in  a  different  plane 
appear.  This  case  is  best  represented  by  Fig.  99,  a  sketch  showing 
an  E.  and  W.  vein  in  a  country  of  slate  striking  N.  and  S.  The 
occurrences  at  Rodna  (Fig.  70)  and  Raibl  (Fig.  69)  furnish  also 
some  illustrations,  though  here  it  is  chiefly  barren  fissures  which 
traverse  and  bend  the  stratification. 

The  text-books  usually  present  only  simple  outline-sketches  of 
such  conditions;  and  accurate  pictures  are  calculated  to  surprise 
those  who  have  not  been  much  in  mines,  by  exhibiting  the  compli- 
cations of  the  actual  occurrences.  (Of  course,  complete  objective 
accuracy  would  require  photographs  of  polished  surfaces.)  I  will 
here  refer  only  to  one  of  the  most  complex  pictures,  shown  in  Fig. 
47  and  taken  from  Weissenbach's  collection  (op.  cit.,  Plate  22).  The 
Gabe  Gottes  vein  of  the  Bescheert  Gliick  mine  at  Freiberg  con- 
sists of  separate  masses  of  decomposed  gneiss,  bounded  by  bar- 
ren fissures,  and  the  stratification  of  which  has  been  disarranged  by 
their  mutual  pressure.  The  fissures  have  no  filling,  but  the  gneiss 
shows  filling,  nearly  representing  its  stratification,  i.e.,  in  planes  al- 
most perpendicular  to  the  walls  of  the  vein.  According  to  my 
view,  the  vein  being  in  this  place  split  up  into  small  fissures,  a 
movement  must  have  occurred,  probably  on  the  lowest  of  these  fis- 
sures shown  in  the  picture;  but  the  result,  instead  of  being  an 
ordinary  fault,  was  a  pulling-apart  of  the  hanging- wall  strata, 
which  created  spaces  perpendicular  to  the  vein-plane,  and  approxi- 
mately between  the  strata.  These  spaces  were  subsequently  filled 
in  the  same  way  as  was  the  simple  main  fissure  itself  in  other  parts 
of  this  vein.  The  case  may  furnish  also  an  explanation  for  certain 
kinds  of  bed-veins. 

The  greater  number  of  ore-veins,  as  of  ore-deposits  in  general, 
occur  in  eruptive  rocks — a  circumstance  which  doubtless  indicates 
that  their  metallic  contents  have  been  derived,  directly  or  indi- 
rectly, through  these  or  other  media,  from  the  barysphere.  The 
most  productive  ore-veins  are  wholly  in  such  rocks,  but  others  occur 
in  stratified  rocks,  traversed  by  eruptives.  Comparatively  few  occur 
wholly  in  stratified  rocks.  In  such  cases  large  faults  have  unques- 
tionably opened  communication  with  the  barysphere.  To  empha- 
size these  relations,  I  will  bring  forward  some  illustrations  from 
well-known  ore- vein  districts  comprising  such  occurrences: 

a.  In  stratified  rocks,  entirely  unconnected  with  eruptives; 


THE   GENESIS   OF   ORE-DEPOSITS.  •  73 

b.  Iii  the  neighborhood  of  eruptive  masses,  and  partially  enclosed 
therein ; 

c.  Wholly  within  large  eruptive  formations. 

a.   Ore-  Veins  in  Stratified  Rocks. 

Genuine  ore-veins  entirely  unconnected  with  eruptive  rocks  are 
not  easily  to  be  found — especially  not  in  cases  of  important  and 
well-studied  districts.  Clausthal,  in  the  Hartz,  still  comes  nearest 
to  fulfilling  these  conditions.  The  Ha^rtz  range  is  a  mass  of  folded 
paleozoic  strata,  which  lifts  itself,  in  lenticular  form,  above  the 
North  German  plateau  of  mainly  Mesozoic  rocks.  The  strata  com- 
prising the  Hartz  generally  strike  at  right-angles  to  the  W.  N.  W. 
direction  of  the  axis  of  the  range,  but  most  of  the  faults  are  ap- 
proximately parallel  to  this  axis,  so  that  the  terms  "  axial "  and 
"  cross  "  mean  here  the  opposite  of  what  they  would  mean  in  ranges 
the  main  axes  of  which  coincide  with  the  strike  of  the  strata. 

Clausthal. — The  ore- veins  of  Clausthal  are  somewhat  peculiar. 
There  are  zones  of  altered  rocks,  20  to  80  meters  (65  to  262  feet) 
wide  and  extending  as  far  as  about  15  km.  (9  miles),  in  which  the 
ore-bodies  are  somewhat  irregularly  distributed.  These  rock-zones 
are  called  vein-clay-slates  (Gangthonschiefer),  to  distinguish  them 
from  the  ordinary  slates  (Culmschiefer)  of  the  district;  and  recent 
uareful  investigations  have  shown  that  their  composition  practically 
corresponds  with  that  of  the  latter.  They  are  therefore  in  fact 
country- rock,  altered  for  the  most  part  mechanically,  and  only  to 
a  slight  extent  chemically.  They  are  foliated;  but  the  foliation 
rather  parallels  the  planes  of  movement,  being  somewhat  steep, 
while  the  strata  of  the  surrounding  region  have  generally  b^t  a 
slight  dip.  These  zones  may  therefore  be  best  conceived  as  the 
result  of  the  friction  of  the  great  masses  which  have  here  been 
rubbed  together. 

In  recent  times,  chiefly  by  A.  von  Groddeck,  it  has  been  actually 
proved  that  these  zones  represent  great  faults,  along  which  either  the 
footwall  mass  was  moved  S.  W.  downward,  or  the  hanging- wall  was 
lifted  N.  E.  The  vertical  movement,  measured  at  certain  points, 
would  be  about  400  meters  (1312  feet);  but  it.  is  probable  that  the 
movement  of  one  mass  upon  the  other  did  not  follow  the  true  dip, 
and  that  the  horizontal  component  was  much  greater  than  the 
vertical.  The  faulted  portions  of  a  kersantite  vein  discovered  by 
Groddeck  show  that  each  southern  mass  was  moved  further  west,  or 
each  northern  mass  further  east. 


74  THE   GENESIS   OF  ORE-DEPOSITS. 

The  network  in  these  zones  of  dislocation  is  also  peculiar.  As 
indicated  in  Fig.  37,  lenticular  masses  have  been  isolated,  after 
undergoing  severally  a  movement  in  the  direction  of  the  axis  of  the 
Hartz  range ;  so  that  the  whole  zone  of  lenticular  masses  expresses 
the  displacement  which  the  solid  crust  has  experienced.  The  struc- 
tural significance  of  the  zones  is  thus  clearly  disclosed,  as  a  means  of 
communication  with  a  deep  region  from  which  the  mineral  solutions 
ascended,  to  deposit  ores  in  the  fissures  of  dislocation.  As  I  have 
already  remarked,  an  ore-vein*  is  thus  represented  as  the  boundary  of 
a  displaced  rock-mass,  and  so  is  brought  into  direct  structural  relation 
with  the  country-rock. 

A  glance  at  the  geological  map  of  the  Hartz  Mountains  will  show, 
however,  that  even  this  region  is  not  free  from  eruptive  rocks  ;  for 
the  stratified  formations  crossing  the  mountain  axis  are  traversed  by 
masses  of  granite,  which  have  evidently  played  a  part  in  the  build- 
ing-up of  the  range  above  the  plateau.  Moreover,  according  to  the 
investigations  of  Dr.  K.  A.  Lossen,*  and  others,  contact- metamor- 
phosis of  the  stratified  rocks  has  proceeded  from  them.  E.  Kayserf 
fixes  the  elevation  of  the  granite  between  the  end  of  the  Carboni- 
ferous and  the  beginning  of  the  Permian,  and  since  several  of  the 
faults  extend  into  this  rock,  he  thinks  it  cannot  have  been  a  factor 
in  the  fissure-formation.  Lossen,  on  the  other  hand,  is  inclined  to 
ascribe  to  the  granite  an  active  part  in  the  formation  of  the  ore- 
deposits,  and  (if  T  understand  him  correctly)  to  believe  that  these 
deposits  were  influenced  by  their  position  against  the  granite  nucleus 
of  the  Hartz  Mountains,  which  is  said  to  lie  steep  on  one  side  and 
more  flat  on  the  other,  beneath  the  sedimentary  strata. 

Accurate  geological  surveys  of  the  Hartz  have  noted  a  large 
number  of  fault- fissures,  some  of  which  connect  the  two  great  ore- 
deposits  of  Clausthal  and  Andreasberg.  Those  which  are  called 
Ruscheln  resemble  the  dislocation-zones  of  Clausthal.  They  are 
fissures,  up  to  30  meters  (108  feet)  wide,  approximately  parallel 
with  the  mountain-axis,  and  filled  with  a  clayey  or  fragmentary 
material,  full  of  striations  and  slickensides  and  generally  of  dark 
color. 

Andreasberg. — Roughly  parallel  with  these  Ruscheln  run  the 
silver-ore  veins  of  Andreasberg,  which  carry  ore  only  on  one  side 

*  "Geol.  u.  petrogr.  Beitrage  znr  Kenntniss  des  Harzes,"  Jahrb.  der  k.  preuss. 
geol.  Landesansta't  ii.  Beryak  filr  1881,  p.  47. 

f  "Ueber  d.  Spaltensystem  am  S.  W.  Abhang  des  Brockenmassivs,"  etc.,  Ibid., 
p.  452. 


THE   GENESIS   OF   ORE-DEPOSITS.  75 

of  the  Ruseheln,  and  lose  their  ore  when  they  approach  the  latter. 
It  was  formerly  imagined  that  the  two  main  Ruseheln  enclosed  a 
lenticular  mass  of  the  country,  to  which  the  silver-ores  were 
confined;  and  H.  Credner*  still  expresses  this  view.  But  Kayser 
(op.  cit.j  p.  443)  observes  that  the  mines  have  disclosed  a  convergence 
of  the  Rascheln  to  the  west  only,  and  that  a  similar  convergence  to 
the  east  has  been  purely  assumed  from  analogy,  whereas  the  surface- 
indicati6*ns  are  rather  those  of  a  wider  separation  in  that  direction. 
(See  Fig.  38.) 

We  have  here  a  case  in  which  the  ores  occupy,  not,  as  in  Glaus- 
thai,  a  previously  prepared  zone  of  dislocation,  but  a  network  of 
veins.  H.  Credner  has  pointed  out  that  the  mineral  solutions  were 
unable  to  penetrate  the  walls  of  the  dislocation-zones,  and  conceived 
in  this  connection  that  these  walls  enclosed  a  lenticular  body  of  rock. 
But  the  main  question  concerns  the  origin  of  the  more  recent  net- 
work of  fissures.  We  must  assume  that  when  the  dislocation-zones 
were  formed,  the  mineral  solutions  had  no  opportunity  to  enter  them, 
because  (as  was  the  case  in  many  great  faults,  e.g.,  those  of  Przi- 
bram)  no  spaces  of  discission  were  formed.  Afterwards,  however,  a 
second  system  of  fissures  originated,  adjusting  itself  to  the  conditions 
created  by  the  first,  and  producing  rock-fragments,  the  relatively 
slight  movement  of  which  did  not  fill  the  interstitial  spaces  with  the 
detritus  of  friction. 

But  outside  of  the  angle  between  the  Ruscheln,  there  are  also  veins, 
which,  considering  their  direction,  may  be  continuations  of  the  silver- 
veins  inside,  although,  being  differently  filled,  they  are  not  so  re- 
garded. 

It  was  formerly  attempted  to  connect  two  eruptive  rocks  with  the 
formation  of  these  ore-veins;  the  granite  which  appears  to  the  north, 
beyond  the  fault-fissures ;  and  the  diabase  which  touches  them  at 
many  points  to  the  south.  The  latter,  however,  is  now  considered 
to  be  a  stratified  layer  in  the  series  of  the  country.  Both  rocks  have 
been  passive  in  the  formation  and  the  filling  of  the  fissures,  and  we 
must  look  again  to  the  deep  region  as  the  source  of  the  ores. 

b.   Ore-  Veins  in  the  Neighborhood  of  Eruptive  Masses. 
The  Erzgebirge. — It  would  be  impossible  here  to  pass  in  review 
the  innumerable  veins  of  the  Erzgebirge  in  Saxony  and  Bohemia. 
Such  a  review  will  soon  be  furnished  by  the  publication  of  a  work 

f  "Geogn.  Beschreib.  d.  Bergw.  distrikts  von.  Andreasberg,"  Zeitsch.  d.  deutsch 
geol.  Gesell.,  xvii.,  p.  221. 


76  THE   GENESIS   OF   ORE-DEPOSITS. 

on  this  subject  by  the  eminent  Saxon  mining  geologist,  H.  Miiller 
(who  has  received  the  honorary  title  of  "Gangmiiller,"  to  distinguish 
him  from  the  many  other  Mullers  of  Germany).  In  this  region, 
veins  in  the  greatest  variety  occur  in  gneiss,  with  here  and  there  an 
eruptive  dike;  but  the  latter  can  scarcely  be  considered  as  more 
than  indications  of  a  former  communication  with  the  barysphere. 

Besides  different  porphyries  and  diorites,  there  is  an  occasional 
dike  of  basalt.  At  Joachimsthal,  in  Bohemia,  we  can  recognize 
pre-  and  post-basaltic  ore-deposition.  We  find  here,  as  in  many 
other  districts,  two  vein-systems  at  right  angles  ;  one  striking  N.-S., 
and  accompanied  with  porphyry  dikes;  the  other  striking  E.— W., 
and  accompanied  with  dikes  of  basalt  and  (according  to  recent  views) 
phonolite.  The  E.-W.  fissures  are  occupied  partly  by  basaltic  dikes, 
partly  by  ore- veins  which  were  deposited,  some  before  and  some 
after  the  basalt,  a.  satisfactory  proof  that  the  fissures  were  formed  at 
the  period  of  basaltic  eruption.  How  far  the  basalt  took  part  in  the 
ore-deposition,  however,  has  not  yet  been  shown. 

In  the  basaltic  and  "  basal t-wacke  "  dikes  of  this  district,  at  the 
considerable  depth  of  some  300  meters  (984  feet)  below  the  surface, 
petrified  tree-trunks  were  found,  a  fact  which  furnishes  an  analogy 
to  the  reported  discoveries  in  the  Bassick  mine  in  Colorado. 

Przibram. — An  entirely  different  picture  is  presented  by  Przibram 
in  central  Bohemia,  where  we  encounter  not  only  a  great  structural 
fault,  but  also  eruptive  dikes,  which  are  followed  by  most  of  the 
ore- veins. 

In  central  Bohemia  the  general  strike  is  NE.-SW.  for  all  rocks 
except  the  diorite  dikes,  which  strike  N. — S.,  thus  varying  45°  from 
the  prevailing  direction.  Above  the  granite  lies  first  a  formation  of 
pre-Cambrian  slates ;  upon  this  follows  unconformably  the  Cambrian 
system,  consisting  below  of  conglomerates  and  sandstones,  and  above 
of  fossiliferous  slates.  Sections  across  the  strike  show  repetitions  of 
the  pre-Cambrian  and  Cambrian  strata  due  to  great  faults,  which 
likewise  strike  NE.-SW.  (Fig.  40). 

The  one  main  fault  which  has  been  exposed  by  mining  to  the 
depth  of  1110  meters  (3600  feet)  is  properly  a  so-called  Weclisel,  by 
which  the  older  stratum  (in  the  hanging- wall  of  the  fault)  has  been 
slid  over  the  later  stratum  (in  the  foot-wall).  Several  other  faults, 
similar  in  character,  though  not  explored  on  an  equal  scale,  occur 
in  the  district;  and  it  may  be  imagined  that  before  this  shoving  to- 
gether of  the  Palaeozoic  strata  of  central  Bohemia  they  must  have 
occupied  a  much  larger  area  than  at  present. 


THE   GENESIS    OF    ORE-DEPOSITS.  77 

This  main  fault,  called  the  "  LettenMuft"  is  constituted  by  a  zone 
of  clay  and  crushed  rock,  from  2  to  10  meters  (6.5  to  33  feet)  wide. 
At  Przibram  itself,  the  sandstones  which  contain  the  ore  are  suc- 
ceeded in  the  hanging-wall  side  by  pre-Cambrian  slates.  A  little 
further  SW.,  at  Bohutin,  granite  appears  on  the  hanging- wall  of 
the  Lettenklufi — evidently,  as  the  cross-section  indicates,  the  granite 
foundation,  here  outcropping  a  second  time,  of  the  whole  palaeozoic 
series. 

Numerous  N.-S.  dikes  occur,  and  in  the  ore-bearing  zone  they  are 
so  close  together  that  some  cross-sections  show  them  to  constitute 
almost  one-third  of  the  total  rock-mass.  The  ore-veins  are  mostly  in 
these  diorite  dikes.  Only  occasionally  do  they  enter  the  stratified 
rocks,  returning  soon  to  the  dikes  they  have  left,  or  to  otflers  of  the 
group.  In  dip  also  they  mainly  follow  the  dikes,  so  that  we  may 
here  assert  with  confidence  that  the  already  existing  dikes  deter- 
mined the  formation  of  the  ore-bearing  vein-fissures. 

As  already  narrated  in  Part  I.,  this  district  was  made  a  test  of 
Sandberger's  lateral-secretion  theory.  Careful  and  repeated  analysis 
showed  the  presence  of  metals  in  the  rocks,  but  could  not  decide  the 
question  whether  these  metals  were  primitive  ingredients  or  sec- 
ondary impregnations.  Since  such  metallic  traces  occur  in  both  the 
eruptive  and  the  sedimentary  rocks,  but  cannot  possibly  be  in  both 
cases  primitive,  it  is  probable  that  they  are  in  both  cases  secondary. 
There  is  then  in  this  case,  notwithstanding  the  connection  of  the  ore- 
veins  with  the  dikes,  no  proof  that  they  were  formed  by  the  leach- 
ing of  the  country-rock.  If  the  vein-material  (as  is  very  likely), 
was  derived  from  eruptive  rocks,  these  were  situated  much  deeper 
than  the  eruptive  rock  disclosed  down  to  1110  meters  (3600  feet) 
below  the  surface,  or  500  meters  (1640  feet)  below  sea-level. 

The  Cambrian  sandstone  basin  of  Przibram  is  unsym metrical ;  one 
side  clips  gently  northwest,  the  other  (next  to  the  fault)  slightly 
southeast.  In  the  latter  part,  which  is  also  more  highly  metamor- 
phosed, lies  the  bonanza  or  rich  ore-ground,  which  therefore  starts 
from  the  intersection  of  the  great  structural  fault  icith  the  zone  of  erup- 
tive rocks,  in  other  words,  from  the  point  relatively  nearest  to  the 
barysphere. 

In  the  steeply-dipping  sandstone  series,  certain  strata  are  petro- 
graphically  characteristic;  and  when  these  are  traced  to  the  inter- 
secting dikes,  it  becomes  clear  that  the  latter  (and  hence  the  ore- 
veins  also),  are  fissure-faults.  Thus  Fig.  39,  a  section  through  the 
Franz  Joseph  shaft,  shows  dislocations  of  the  strata  (adinole-beds) 
as  great  as  about  200  meters  (656  feet). 


78  THE   GENESIS   OF   ORE-DEPOSITS. 

It  should  be  added,  that  the  dikes  present  different  kinds  of  erup- 
tive rock,  and  that  they  are  generally  decomposed  in  the  neighbor- 
hood of  the  ore-veins — a  result  naturally  to  be  attributed  to  the 
action  of  the  mineral  springs;  also,  that  stratified  rocks  show,  near 
the  granites,  a  contact-metamorphosis  which  has  converted  them  into 
hornstone.  This  phenomenon  recalls  the  Hartz,  especially  the  St. 
Andreasberg  district. 

c.   Ore-  Veins  Wholly  Within  Large  Eruptive  Formations. 

Hungary. — If  we  turn  to  Hungary,  we  find  many  veins  wholly 
included  in  eruptive  rocks.  One  of  the  best  known  districts  is  that 
of  Schemnitz,  which  presents  in  geological  conditions  the  nearest  ana- 
logue of  the  Washoe  district  and  the  Comstock  lode  in  Nevada. 

In  both  cases,  various  eruptives,  principally  Tertiary,  such  as 
diorite,  andesite,  trachyte  and  rhyolite,  ranging  to  basalt,  are  spread 
over  a  Mesosoic  (mainly  Triassic)  foundation.  The  N.  and  S. 
extension  of  these  masses  and  of  the  ore-veins  they  contain  is  alike 
in  both  districts.  The  number  of  veins  at  Schemnitz  is  very  large, 
and  they  exhibit  a  very  great  variety  of  filling.  In  some  of  them, 
so-called  "  ore-columns,"  i.e.,  specially  rich  ore-channels  (chimneys  or 
shoots),  have  been  recognized.  Those  in  the  Gruner  vein,  according 
to  M.  V.  Lipold,*  are  short  horizontally,  but  much  prolonged  in 
the  direction  of  their  pitch,  obliquely  on  the  dip  of  the  vein.  In 
other  ore-veins,  e.g.,  in  the  Spitaler  master-lode,  which  is  about  40 
meters  (131  feet)  wkle,  and  has  been  traced  for  8  km.  (5  m.);  also 
in  the  Bieber  and  other  veins,  the  ore- bodies  are  said  to  have  covered 
large  areas  of  the  vein-sheet.  The  ore  richest  in  goll  is  reported 
to  be  the  so-called  Zinnopel,  a  crust  consisting  of  jasper,  with 
pyrite,  chalcopyrite  and  galena,  which  surrounds  fragments  of  an 
earlier  quartz  crust. 

In  the  trachyte  range  of  Vihorlat  Gutin,  which  runs  NW.  and 
SE.,  approximately  parallel  with  the  Hungarian  boundary,  there  is 
a  series  of  gold  and  silver  mining  districts,  containing  occasional 
large  veins  with  numerous  small  ones.  Among  the  former  are  those 
of  Nagybanya  and  Felsobanya,  where  several  domes  of  trachyte  or 
of  andesite,  breaking  through  the  late  Tertiary  "  Congerien"  strata, 
are  in  turn  traversed  by  large  veins,  which  split  up  near  their  out- 
crops, so  as  to  exhibit  in  vertical  cross-section  a  fan-shaped  arrange- 
ment. 

*  "  Der  Bergbau  von  Schemnitz  in  Ungarn,"  Jahrb.  d.  k.  k.  geol.  R.  Anstalt., 
1867,  p.  403. 


THE   GENESIS   OF   ORE-DEPOSITS.  79 

Further  east  is  the  Kapnik  mining  district,  containing  a  series  of 
separate  veins ;  then  comes  Rota,  similar  in  character;  and  finally 
(over  the  line  in  Transylvania),  the  district  of  Olahlaposbanya,  the 
veins  of  which  are  partly  in  the  eruptive  rock,  partly  in  the  old  Ter- 
tiary strata  which  it  traverses. 

Throughout  the  range,  silver-ores  predominate,  occasionally  with 
a  considerable  gold-value.  In  the  eastern  portion,  copper-ores 
appear. 

The  Dacian  Gold-Field. — In  southwestern  Transylvania,  in  the 
Dacian  gold-district,  all  the  gold-mines  are  grouped  in  connection 
with  four  separate  eruptive  zones  of  recent  origin.  The  main  rock 
of  the  region  is  Cretaceous  sandstone,  with  occasional  exposures  of 
Jurassic  and  Triassic  strata,  the  latter  of  which  include  heavy  out- 
flows of  melaphyre,  and  also  masses  of  crystalline  rocks.  The 
recent  eruptives,  comprising  porphyry,  diorite,  andesite,  basalt,  etc., 
occur  in  a  triangle,  the  base  of  which  is  formed  by  the  widest  range, 
the  Cietrasian,  which  strikes  NW.  and  SE.,  and  in  which  are  the 
mines  of  Nagyag,  Magura,  Fiizesd,  Boiza  and  Ruda.  In  a  second, 
approximately  parallel  range,  are  the  mines  of  Faczebaja  and 
Almas;  in  a  third,  those  of  Yulkoj  and  Verespatak  and  in  a  fourth, 
forming  the  apex  of  the  triangle,  those  of  Offenbanya  * 

These  mines,  which  are  for  the  most  part  very  ancient  (pre-Roman), 
I  shall  treat  fully  in  a  monograph  now  in  course  of  preparation.  In 
the  whole  Dacian  gold-district  the  predominant  deposits  are  fissure- 
veins,  sometimes  represented  by  mere  "  knife-blade "  seams,  con- 
tinuous for  short  distances  only.  In  some  places,  as  in  the  celebra- 
ted Verespatak  district,  other  types  of  deposit  are  represented,  the 
ores  of  which,  however,  also  occur  in  spaces  of  discission,  namely,  in 
eruptive  breccias,  between  the  related  fragments,  in  the  form  which 
I  have  elsewhere  called  typhonic  masses ;  but  these  are  ore-bearing 
only  where  they  are  in  contact  with  the  ore-veins.  The  same  is  true 
of  the  conglomerates  into  which  these  breccias  sometimes  pass,  and 
in  which  the  ore  takes  the  place  of  the  interstitial  cement,  as  I  have 
explained  in  a  preceding  chapter,  and  illustrated  in  Fig.  18.  For 
further  elucidation,  I  show  in  Fig.  41  a  breccia,  and  in  Fig.  42  a 
conglomerate.  (It  should  be  observed  that  the  mutual  relation  of 
the  fragments  of  a  breccia  can  be  recognized  only  when  they  have 
not  suffered  much  movement  after  fracture).  In  both  these  speci- 

*  F.  Posepny,  ''  Allgera.  Bild  d.  Erzfuhrung  im  Siebenb.  Golddistrikte,"  Jahrb. 
d.  k.  k.  geol.  R.  Ansiali.,  xviii.,  p.  297. 


80  THE   GENESIS   OF   ORE-DEPOSITS. 

mens,  the  rock  is  quartz-porphyry  with  quartz-crystals  of  pea-size. 
In  Fig.  41  the  interior  of  the  fragments  is  considerably  decomposed, 
whereas  the  exterior  shows  a  thin  layer,  either  of  undecom posed  rock, 
or  of  material  subsequently  impregnated  with  silica  from  the  open 
interstices,  and  thus  made  capable  of  resistance.  Sometimes  the  por- 
phyry is  found  to  be  traversed  by  a  complex  network  of  fissures, 
filled  (except  as  to  some  wider  spaces  of  intersection),  with  a  clastic 
mass,  like  sandstone.  The  interstices  of  the  conglomerate,  Fig.  42 
(except  the  spaces  containing  crusts  of  manganese  spar  and  quartz) 
are  filled  with  a  clastic  cement,  mostly  silicified  into  hornstone. 

This  sort  of  ore-filling  is  comparable  in  some  degree  with  ore- 
deposits  in  soluble  rocks,  when  the  filling  has  passed  from  the  space 
of  discission  proper  into  the  rock,  after  room  has  been  made  for  it  in 
the  latter  by  dissolution.  In  the  cases  before  us  such  room  was 
made  by  the  partial  washing  away  of  the  (probably  clayey)  cement 
of  the  breccias  and  conglomerates. 

Verespalak. — The  gold-district  of  Verespatak  is  situated  at  the 
north  end  of  the  second  eruptive  range.  The  two  porphyry  masses 
of  Kirnik  and  Boi  form  a  center,  around  which  sandstone  and  por- 
phyry-tufa lie  almost  horizontally,  and  in  part  unconformably,  upon 
folded  Cretaceous  sandstones  below.  The  whole  district  is  surrounded 
by  a  zone  of  trachytes,  andesites,  and  their  lavas,  which  once  (as  may 
be  inferred  from  the  fragments  remaining  on  the  porphyry  and  tufa) 
overspread  the  entire  district,  and  have  been  removed  by  erosion, 
laying  bare  the  two  older  eruptive  masses  of  the  porphyry. 

A  funnel-shaped  depression  seems  to  have  been  formed  in  the 
folded  Cretaceous  strata,  from  the  middle  of  which  ascended  the 
porphyry-outflows,  furnishing  also  the  material  for  the  porphyry- 
tufa,  which  fills  this  funnel-shaped  basin. 

The  principal  gold-bearing  rock  is  the  porphyry,  yet  the  tufas  and 
the  Cretaceous  rocks  near  the  porphyry-outflow  carry  gold  ;  whereas, 
no  gold  or  ore  of  any  kind  occurs  in  thetrachyticand  andesitic  lavas 
which  once  covered  the  region. 

Vulltoj. — At  Yulkoj,  however,  at  the  southern  end  of  the  second 
eruptive  range,  almost  the  opposite  is  the  case.  Here  the  older  and 
deeper  quartzose  rock  carries  little  ore,  while  gold  abounds  in  the 
overlying  andesites.  Several  mines  of  the  Dacian  gold-district  have 
encountered  in  depth  the  stratified  rocks  through  which  the  eruptives 
came,  and  the  result  has  generally  been  disastrous  to  the  miner,  the 
ore-veins  having  either  ceased  entirely  or  become  pinched  to  barren 
fissures.  In  the  first  case  it  would  appear  that  the  vein-fissures  had 


THE   GENESIS   OF   ORE-DEPOSITS.  81 

been  formed  by  the  contraction  of  the  eruptive  material.  But,  in 
general,  it  should  be  said  that  these  phenomena  are  by  no  means 
clearly  and  reliably  reported.  The  prejudices  of  the  miners  play 
too  large  a  part  in  their  reports.  This  much  is  certain,  that  any  fis- 
sure, in  passing  from  one  rock  to  another,  is  likely  to  exhibit  a  cer- 
tain irregularity  in  both  direction  and  filling,  and  that  a  change  of 
this  kind  should  not  be  allowed  to  discourage  at  once  all  further 
exploration. 

In  some  cases  there  has  been  found,  below  an  eruptive  rock  con- 
taining ore-veins,  a  decomposed  breccia  of  the  same,  which  was  quite 
barren.  The  great  porphyry  mass  of  Kirnik,  at  Verespatak,  has 
been  pierced  through  and  through  with  ancient  and  modern  work- 
ings, like  the  pores  in  a  sponge.  In  recent  years  deep  adits  have 
been  driven  into  it  to  reach  fresh  ground,  but  with  unsatisfactory 
results.  A  short  time  ago  the  deepest  of  these  adits  encountered  in 
the  nucleus  of  the  Kirnik  mass  not  the  ore-bearing  porphyry;  but 
decomposed  clastic  rock  and  porphyry-breccia,  which  may  be  sup- 
posed to  be  the  filling  of  the  crater-opening.  The  Vulkoj  mass, 
which  has  been  almost  cut  into  two  halves  by  very  ancient  open- 
workings  along  its  crest,  contained  a  series  of  N.  —  S.  veins,  the 
richest  of  which  (the  Jeruga)  was  cut  in  depth  by  adits  from  both 
sides.  On  the  south  side  appears  a  slaty  Cretaceous  rock,  underlying 
the  porphyry,  and  extending  (see  Fig.  43)  upon  the  Jeruga  plane, 
with  two  offsets,  to  the  deepest  adit  on  the  north  side,  where  it  strikes 
the  decomposed  breccias,  in  which  the  very  rich  ores  mined  above 
can  no  longer  be  found  to  continue. 

As  to  the  continuation  of  the  veins  in  the  slaty  rock,  the  follow- 
ing facts  are  pertinent.  West  of  the  Vulkoj  mass,  in  the  sandstones 
and  slates,  there  is  another  gold-field,  that  of  Botesiu,  the  veins  of 
which  are  analogous,  both  in  strike  and  in  ore-filling,  to  those  of 
Vulkoj.  Botesiu  shows  no  eruptive  rocks;  nevertheless,  a  study  of 
the  whole  region  shows  that  the  formation  of  its  vein-fissures  must 
have  been  connected  with  them,  and  it  is  even  not  impossible  that 
they  may  once  have  extended  as  far  as  this,  and  may  have  been  re- 
moved by  subsequent  erosion.  It  follows  that  we  must  assume  the 
Vulkoj  veins  to  extend  below  the  andesite  into  the  slate,  though 
this  has  been  doubted  by  some.  Fig.  44  shows  the  situation  in  an 
E.-W.  section. 

In  the  region  of  Boitza  the  eruptive  zone  (predominantly  of 
quartzose  dacites  or  porphyries)  crosses  an  exposure  of  Mesozoic 
limestones  and  melaphyrs,  and  the  veins  pass  directly  from  the  por- 
phyry into  the  underlying  melaphyr. 

6 


82  THE   GENESIS   OF   ORE-DEPOSITS. 

At  Xagyag,  Magura,  and  Fiizesd,  in  following  the  gold- veins  in 
depth,  masses  of  Tertiary  sandstones  and  conglomerates  are  formed, 
broken  through  and  enveloped  by  the  eruptive  rocks. 

At  four  places  in  the  Dacian  gold-district,  namely,  Oflfenbanya, 
Faczebaja,  Fericiel,  and  Nagyag,  telluric  ores  occur.  In  the  neigh- 
borhood of  Zalatna  there  is  cinnabar,  and  at  several  points  near 
Korosbanya  there  are  copper-ores  carrying  a  little  gold.  Gold  is, 
however,  mainly  connected,  as  has  been  observed,  with  the  four 
ranges  of  Tertiary  eruptives,  and  appears  chiefly  in  these  rocks, 
though  also  in  the  stratified  rocks  which  they  traverse. 

The  occurrence  of  gold  in  this  case  is  thus  somehow  related  to  the 
eruptions;  but  since  I  have  never  found  it  as  a  primitive  or  idio- 
genous  constituent  of  these  rocks,  I  do  not  believe  that  it  was  de- 
rived originally  from  them.  There  is,  therefore,  nothing  left  but  to 
consider  the  eruptions  as  the  agents  of  a  communication  with  the 
deep  region,  from  which  at  these  points  the  mineral  springs  as- 
cended. The  Daciau  gold-district  will  furnish,  upon  further  ex- 
ploration, important  contributions  to  the  inquiry  into  the  original 
source  of  the  gold.  For  instance,  if  the  auriferous  character  of  the 
veins  of  Vulkoj  should  be  found  to  continue  in  the  shaly  sandstones 
underlying  the  andesite,  my  view  would  be  confirmed. 

The  Comstock  Lode. — The  most  thoroughly  studied  American 
vein-phenomena  bearing  on  this  question  are  doubtless  those  of  the 
Comstock  lode.  It  is  not  necessary  to  enter  here  upon  a  detailed 
description.  I  content  myself  with  a  reference  to  the  three  large 
treatises  upon  the  district,*  of  which  Becker  especially  discusses  the 
genetic  question.  To  appreciate  this  question,  however,  some  sim- 
ple illustrations  are  required;  and  these  have  been  compressed  into 
Figs.  58  to  63. 

As  already  observed,  the  general  geological  conditions  of  the  Corn- 
stock  lode  show  a  strong  analogy  to  those  of  the  Schemnitz  district. 
Only  occasional  bodies  of  sedimentary  rocks  are  found,  while  the 
principal  mass  of  the  whole  elevated  region  consists  of  a  great  va- 
riety of  eruptive  rocks,  principally  of  the  more  recent  periods.  The 
altitudes  of  the  more  important  points  above  sea-level  are  about  as 
follows : 

*  Clarence  King,  U.  S.  Oeol.  Explor.  of  the  4Qth  Parallel,  iii.,  Mining  Industry, 
Washington,  1870. 

J.  A.  Church,  The  Comstock  Lode:  Its  Formation  and  History,  New  York,  1879. 

G.  F.  Becker,  "  Geology  of  the  Comstock  Lode,"  etc. —  U.  S.  Oeol.  Survey  Mono- 
graph, Washington,  1882. 


THE   GENESIS   OF   ORE-DEPOSITS.  83 

Meters.  Feet. 

Mount   Davidson  (the  highest  point  of  the  re- 
gion),             2420  7941 

Outcrop  at  the  Gould  and  Curry  mine  (the  datum- 
line  for  measurements  of  depth),    .         .         .        1950  6400 

The  Sutro  Tunnel,  at  different  points,  1840   to      f  1390  4560 

1865  feet  below  datum-line,  ....      1 1382  4535 

The  deepest  point  in  the  Belcher  and  Crown  Point 

shaft,  341 4  feet  below  datum,         .       .-.;-.  '••-.»   -       910  2986 

These  figures  alone  indicate  the  immense  extent  of  the  eruptive 
material. 

The  stratified  rocks  occur  in  a  considerable  continuous  body  at 
Gold  Hill,  in  the  southern  part  of  the  district,  while  in  the  northern 
part  only  a  small  body  enclosed  in  eruptive  rocks  is  found  in  the 
Sierra  Nevada  shaft. 

The  several  eruptive  rocks  have  been  differently  defined  at  differ- 
ent times,  according  to  the  changes  in  petrography  and  in  the 
methods  of  investigation  pursued.  Becker  distinguishes:  1.  Basalt 
(B).  2.  Later  hornblende-andesite  (LHA).  3.  Augite-andesite 
(AA).  4.  Earlier  hornblende-andesite  (EHA).  5.  Later  diabase  or 
black  dyke  (LDb).  6.  Earlier  diabase  (EDbJ.  7.  Quartz-porphyries 
(QP).  8.  Metamorphosed  diorites  (MDr).  9.  Porphyritic  diorites 
(PDr).  10.  Granular  diorites  (GDr).  11.  Metamorphic  rocks 
(M).  12.  Granites  (G).  This  classification  is  based  upon  careful 
microscopic  examination.* 

The  two  principal  veins  (the  Comstock  and  the  Occidental)  strike 
N.  S.,  and  the  Comstock  has  been  traced  5  or  7  km.  (3  or  4  m.), 
according  as  its  branches  are  omitted  or  included  in  the  measure- 
ment. The  position  and  the  branching  of  the  veins  are  shown  in 
the  sketch-map,  Fig.  58,  in  which  the  two  most  important  eruptive 
rocks,  the  diorite  and  the  diabase,  are  emphasized  by  shading,  the 
others  being  indicated  by  letters,  as  in  the  above  list.  The  diorite 
forms  the  foot-wall  from  Gold  Hill  to  Virginia  City.  South  of  Gold 
Hill  metamorphic  slates  form  the  foot-wall,  and  even  extend  across 
in  part  to  the  hanging-wall  side,  as  does  the  diorite  to  the  north  of 
Virginia  City.  Moreover,  in  one  place  a  dike  of  diabase — the  so- 
called  "  black  dike," — occurs  immediately  on  the  foot-wall. 

*  Messrs.  Arnold  Hague  and  J.  P.  Iddings  (Butt.  17,  U.  S.  Geol.  S.,  1 885,  "  On  the 
Development  of  Crystallization  in  the  Igneous  Rocks  of  Washoe,"  etc.),  have  stated 
as  their  conclusion  that  GDr,  EDb  and  AA  are  identical ;  PDr  is  EHA ;  MDr  is 
LHA  ;  and  LDb  is  B  ;  apparent  differences  being  due  to  conditions  of  cooling.  In 
Butt.  No.  6,  Cal.  Acad.  of  Sc.,  1886,  Mr.  Becker,  after  a  reinvestigation  of  the  lo- 
cality, denies  this  conclusion  in  toto,  so  far  as  the  Comstock  rocks  are  concerned. 


84  THE   GENESIS   OF   ORE-DEPOSITS. 

The  hanging-wall  is  principally  diabase,  at  least  in  depth.  In 
the  upper  region  it  is  sometimes  covered  with  other  eruptives,  most 
frequently  with  hornblende-andesite. 

On  the  whole  (with  variations  at  some  places),  the  Comstock  pre- 
sents wide,  gently-dipping  masses,  predominantly  of  crushed  and 
decomposed  country-rock,  and  enclosing  large  flat  "  horses  "  of  the 
same.  The  filling  is,  as  a  rule,  saccharoidal  granular  quartz  (some- 
times more  compact),  in  which  the  ores  are  very  finely  disseminated. 
At  some  points  they  have  occurred  concentrated,  forming  the  bo- 
nanzas to  which  the  colossal  gold-  and  silver-production  of  the  dis- 
trict is  due.  The  ores  are  silver-ores  (stephanite,  polybasite,  argen- 
tite),  with  sometimes  galena  and  zinc-blende.  The  bullion  produced 
from  them  contains  about  half  its  value,  or  6  td  7  per  cent,  of  its 
weight,  in  gold. 

Some  of  these  bonanzas  were  in  the  upper  region  and  came  to  the 
surface.  Others  (like  the  richest  one  of  all,  in  the  Consolidated 
Virginia  and  California  mine)  were  found  in  the  deep  region  ;  and 
it  is  asserted  that  they  were  limited  on  all  sides,  without  connection 
with  other  ore-bodies.  This  would  make  them  unlike  our  ore-chan- 
nels or  chimneys,  which  usually  do  have  interconnection.  But  I  can- 
not conceive  of  their  formation  in  any  other  way  than  upon  the  hy- 
pothesis that  in  such  places  more  open  spaces  existed,  through  which 
larger  quantities  of  dilute  metallic  solutions  passed  and  made  de- 
posits. 

The  distribution  of  the  bonanza-areas  upon  the  vein-area  is  quite 
irregular;  and  it  has  not  been  possible  hitherto  to  trace  any  connec- 
tion between  the  bonanzas  and  the  petrographic  or  structural  condi- 
tions in  their  vicinity.  In  form  they  are  equally  without  any  law, 
as  far  as  has  yet  been  observed.  The  bonanzas  of  the  Con.  Ya. 
and  Cal.  consisted  of  a  main  body  and  three  lenticular  masses  higher 
up,  which,  taken  together,  have  a  flat  pitch  to  the  north.  The 
bonanza  between  Belcher  and  Yellow  Jacket,  on  the  other  hand, 
followed  the  true  dip  of  the  vein  ;  while  the  bonanza  in  Justice — a 
mine  on  the  NW.-SE.  branch,  which  dips  NE.  much  less  steeply 
than  the  main  lode — shows  again  a  north  pitch. 

This  NW.-SE.  branch  of  the  Comstock  shows  a  filling  different 
in  some  respects  from  that  of  the  main  lode,  and  may  be  considered 
as  a  cross- vein,  running  into  the  Comstock,  or  into  the  black  dike 
which  accompanies  its  footwall.  (Becker's  atlas,  ix.) 

In  the  Justice  mine,  namely,  the  filling  is  mostly  calcite,  with 
little  quartz,  instead  of  quartz  with  very  subordinate  calcite,  as  in 
the  main  lode.  According  to  Becker  (1.  c.,  p.  219)  the  calcitic  filling 


THE   GENESIS   OF   ORE-DEPOSITS.  85 

is  characteristic  of  the  whole  SE.  branch.  According  to  Church, 
(op.  tit.,  173)  compact  crusts  of  calcite  alternate  in  the  Justice  mine 
with  their  quartz  crusts.  This  is  the  only  clear  report  of  crustifica- 
tion  any  where  on  the  Comstock.  (I  believe,  however,  that  I  was 
able  to  observe  upon  a  rich  specimen  from  the  Con.  Va.  bonanza, 
after  polishing,  a  parallel  structure  in  the  mineral  aggregate.  I 
received  this  specimen  in  1876  from  Mr.  Fair,  one  of  the  "  bonanza 
kings,"  as  a  sort  of  compensation  for  the  refusal  to  permit  me  to 
enter  the  then  rich  mine  !) 

A  comparison  of  the  many  cross-sections  of  the  Comstock 
published  by  King,  Church  and  Becker,  and  representing,  of 
course,  various  stages  of  knowledge  of  the  vein,  shows  that  no 
normal  or  average  section  can  be  given,  because  the  condition  at 
different  points  on  the  strike  are  so  different,  and  at  some  places, 
e.  g.  the  junctions  of  the  branches,  developments  have  not  given 
satisfactorily  complete  exposures.  The  sections,  Figs.  59  to  63,  are 
given  (on  a  scale  too  small  to  show  much)  merely  to  illustrate  the 
distribution  of  the  country-rocks.  They  are  reduced  from  Becker's 
monograph.  In  the  three  northerly  sections  the  footwall  is  granular 
diorite ;  in  the  two  southern  (Yellow  Jacket  and  Belcher),  and  along 
the  SE.  branch,  it  is  metamorphic  slate.  In  the  southern  portion, 
the  so-called  black  dike  (according  to  Becker,  later  diabase)  appears 
on  the  foot- wall,  and  follows  the  vein  beyond  the  point  where  the 
SE.  branch  leaves  it.  The  hanging- wall  is  diabase,  except  at  the 
northern  end,  where  diorite  becomes  the  hanging-wall  as  well  as  the 
footwall.  In  the  upper  region,  however,  earlier  diabase  is  covered 
by  other  eruptives.  Diabase  is  the  hanging-wall  of  the  SE.  branch 
also ;  but  in  the  footwall  of  that  branch,  besides  the  metamorphous 
slates,  granular  diorite  and  quartz-porphyry  appear. 

So  far  as  the  sources  of  the  eruptive  rocks  can  be  inferred,  they 
were  all  (except  that  of  the  diorite)  on  the  hanging-wall  side  of 
the  vein,  as  were  also  the  mineral  springs  which  subsequently 
decomposed  these  rocks.  But  the  ascending  thermal  waters  encoun- 
tered in  these  mines  were  within  the  vein  itself;  whence  it  may  be 
concluded  that  the  ore-bearing  solutions  came  by  that  road  from  the 
deep  region,  and  not,  according  to  the  lateral-secretion  theory,  from 
the  side.  In  other  words,  the  Comstock  ores  were  not  washed  from 
those  rocks  which  have  been  mined  between  1950  and  910  meters 
(7,941  and  2,986  feet)  above  sea-level,  but  from  material  lying 
much  deeper. 

The  investigations  of  G.  F.  Becker  were  made  at  a  time  when 


86  THE   GENESIS   OF   ORE-DEPOSITS. 

importance  was  still  attached  to  Sandberger's  theory,  and  the 
correctness  of  his  method  of  inquiry  was  assumed.  The  matter 
takes  a  different  aspect  when  we  (quite  justifiably)  doubt  whether 
the  minute  metallic  admixtures  detected  by  wet  or  dry  analysis  were 
originally  in  the  rock,  and  acknowledge  that  they  may  possibly  have 
entered  it  afterwards.  This  is  evidently  the  case  with  the  precious 
metals  in  the  pyrite  of  the  ore-bearing  rock.  That  this  pyrite  is  a 
secondary  impregnation  can  be  proved  with  the  microscope,  and  is 
admitted  by  Becker  also.  In  my  opinion,  any  eruptive  rock  may 
give  rise  by  metamorphosis  to  the  type  which  we  call  in  Hungary, 
greenstone,  greenstone-trachyte,  etc.,  and  which  F.  von  Richthofen 
named  propylite,  because  of  its  frequent  occurrence  as  the  country- 
rock  of  ore-deposits.  Whether  the  precious  metals  can  be  detected 
in  this  rock  depends  wholly  upon  its  impregnation,  or  that  of  one  of 
its  constituent  minerals,  with  pyrite.  But  it  does  not  follow  that 
this  was  the  primitive  condition.  From  this  standpoint  are  to 
be  regarded  the  metallic  values  reported  by  Becker,  and  here 
reduced,  for  the  sake  of  better  understanding,  from  cents  per  ton  to 
grammes  per  1000  kilograms.  A  pyrite  washed  from  decomposed 
diabase,  near  the  face  of  the  north  branch  of  the  Sutro  tunnel,  con- 
tained 3  cents  silver  and  8  cents  gold,  i.e.,  0.72  grm.  silver  and  0.12 
grm.  gold,  per  metric  ton.  The  pyrite  from  the  slates  in  the  Belcher 
mine  carried  even  18  c.  (4.32  grm.)  silver  and  20  c.  (0.30  grm.)  gold. 
Fresh  diabase  is  said  to  have  contained  4  to  5  c.  (0.6  to  0.7  grm.) 
gold  ;  the  diorite  of  Bullion  ravine,  only  a  trace;  while  the  andesite 
yielded  about  as  much  as  the  diabase.  Augite  separated  by  Thoulet's 
method  from  the  diabase  was  found  to  be  eight  times  as  rich  as  a 
corresponding  quantity  of  the  feldspar. 

Comparative  investigations  are  reported  to  have  shown  that  the 
decomposed  diabase  contains  only  half  as  much  silver  as  the  fresh — 
a  circumstance  which  was  interpreted  in  favor  of  the  lateral -secre- 
tion theory,  on  the  assumption  that  the  decomposed  diabase  had 
given  up  half  its  silver  to  the  vein-filling. 

Since  the  diorite  in  the  upper  portion  of  Bullion  ravine  shows 
only  traces  of  silver,  but  at  the  mouth  of  the  ravine,  near  the  vein, 
contains  a  considerable  amount,  Becker  considers  this  indicative 
rather  of  an  impregnation  of  the  rock  proceeding  from  the  vein. 

Moreover,  the  andesites  and  quartz-porphyries  also  contain  small 
amounts  of  silver;  while  the  strongly  calcareous  raetamorphic 
diorite  carries  8  c.  (1.92  grms.)  per  ton,  which  might  be  connected 
with  the  vein-filling  in  the  Justice  mine.  Finally,  the  basalt  con- 


THE   GENESIS   OF  ORE-DEPOSITS  87 

tains  nearly  as  much  silver  as  the  older  diabase ;  but  the  basalt 
cannot  be  cited  as  a  source,  because  it  comprises  the  freshest  rock  in 
the  district,  and  shows  no  trace  of  decomposition  in  its  olivine 
(Becker,  /.  c.,  pp.  223-225).  These  facts  would  be  favorable  to  the 
notion  of  lateral  secretion,  if  only  it  could  be  proved  at  the  same 
time  that  the  metalliferous  character  was  primitive.  But  our 
knowledge  does  not  go  so  far  as  that ;  and  the  Comstock,  like  the 
deep  mines  of  Przibram,  ceases,  therefore,  to  be  a  proof  of  the 
lateral-secretion  theory. 

The  Comstock  differs  in  many  respects  from  typical  ore-veins.  It 
is  properly  a  quartz-vein,  in  which,  at  various  points,  important 
ore-concentrations  have  been  formed,  not  showing  (except  in  the 
Justice  mine)  any  clear  crustification,  though  this  may  have  been 
present  at  some  time,  and  may  have  been  obliterated  by  metamor- 
phosis of  the  vein-mass,  e.g.,  through  the  replacement  of  calcite  by 
quartz.  It  is  also,  in  the  main,  a  contact-vein,  between  a  diorite 
foot-  and  a  diabase  hanging-wall,  with  steep  spurs  running  upward 
into  the  diabase  and  traversing  also  still  more  recent  eruptives.* 
Some  of  these  peculiarities  are  represented  in  other  districts. 

2.  ORE-DEPOSITS  IN  SOLUBLE  ROCKS. 

In  this  group  we  shall  find  two  genetic  types  represented :  the 
fillings  of  spaces  of  dissolution,  and  the  metasomatic  deposits,  the 
origin  of  which  will  be  particularly  considered,  together  with  some 
related  metamorphic  deposits  in  soluble  rocks,  which  have  not  yet 
been  sufficiently  studied  to  be  classed  apart. 

The  expression  "soluble  rock  "is  to  be  understood  in  its  ordinary 
sense  of  solubility  in  the  waters  commonly  represented  on  the 
earth's  surface.  Acid  and  caustic  waters  will  attack,  more  or  less, 
nearly  all  rocks,  though  not  so  as  to  dissolve  them  completely,  as 
we  see  limestone  dissolved.  I  include  especially  among  the  soluble 
rocks,  rock-salt,  gypsum,  limestone,  and  dolomite.  Of  the  following 
instances  I  shall  describe  most  fully  those  which  I  have  personally 
studied,  giving  only  the  essential  outlines  of  other  related  occur- 
rences. 

Rodna. — The  ore-deposit  of  Rodna,  in  NE.  Transylvania,  is 
interesting  to  me  (apart  from  analogies  which  it  offers  with  Lead- 
ville.  Colo.),  as  the  first  in  which  I  had  the  opportunity  to  study  the 
origin  of  an  ore-deposit  by  replacement. 

It  is  situated  on  the  line  of  two  andesite  ranges,  having  a  com- 

*  This  is  denied  by  Hague  and  Iddings,  op.  cit.  p.  41. — See  foot-note  on  p.  83  of 
this  paper. 


88  THE   GENESIS   OF   ORE-DEPOSITS. 

mon  strike, — the  Hungarian  Vihorlat  Gutine,  stretching  NW., 
and  the  Transylvanian  Hargitta  range,  running  SE., — and  at  the 
point  where  this  line  cuts  through  the  mass  of  the  Rodna  Alps. 
The  predominant  rock  is  mica-slate,  with  numerous  intercalations  of 
limestone,  and  is  traversed  by  many  dikes  and  masses  of  andesite. 
Ore-deposits  have  been  found  at  many  points  in  the  district.  The 
most  important,  situated  in  the  Benyes  mountain,  was  carefully 
studied  by  me  in  1862,  after  the  ore-bodies  in  the  mine  had  been 
worked  out.  J.  Grimm  had  examined  the  mine  in  1834,  and  had 
considered  the  deposits  to  be  primitive  beds  at  the  contact  between 
limestone  and  mica  slate,  and  to  have  occupied  that  position  before 
the  andesite  eruption,  by  which  they  had  been  much  shattered. 

The  ores  (pyrites,  black  zincblende,  and  argentiferous  galena, 
slightly  auriferous,  with  quartz  and  calcite)  often  occurred,  it  is  true, 
on  the  gently-dipping  contact- planes;  but  in  certain  E.  and  W. 
lines  they  stood  steeply,  much  like  veins.  In  these  places  the  flat 
deposit,  and  with  it  the  stratification,  had  suddenly  turned  upward 
and  it  was  clear  to  me  that  the  occurrence  represented  a  peculiar 
form  of  fault,  namely,  a  bending  of  the  strata,  followed  by  fracture 
in  the  direction  of  the  dislocating  force,  when  the  limit  of  cohesion 
had  been  passed.  Here  and  there,  in  these  steep  places,  the  stopes 
had  been  carried  beyond  the  contact,  and  the  resulting  appearance 
was  as  if  the  steep  deposit  had  been  the  primary  one,  and  had  sup- 
plied the  ore  to  the  contact.  Occasionally  eruptive  breccias  were 
observed  along  the  steep  deposits.  At  lower  levels,  in  the  down- 
ward continuation  of  the  fissure  of  the  steep  deposit,  eruptive  rocks 
and  thin  breccias  occurred ;  and  these  became  predominant  in  the 
lowest  part  of  the  mine. 

The  structure  of  the  ore-beds  was  mainly  massive,  and  not  crusti- 
fied.  In  some  places,  however,  druses  had  been  developed,  which 
showed  the  same  paragenetic  succession  as  the  mass  of  the  bed,  and 
which  contained  pseudomorphs  of  pyrite  and  galena  after  calcite. 
The  thickness  of  the  ore-bed  was  extremely  variable,  the  greater 
part  of  the  contact-area  being  scarcely  worth  working,  while  at  sin- 
gle points  colossal  masses  of  ore  were  found.  These  circumstances 
led  me  to  consider  the  deposits,  not  as  contemporaneous  in  origin 
with  the  rock,  but  as  subsequently  formed  by  the  circulation  of 
mineral  waters  along  the  contact-planes.  In  other  respects  I  adopted 
at  that  time  the  explanation  of  J.  Grimm.* 


*  Some  results  of  my  studies  at  Rodna  will  be  found  in  the  Verhandlunyen  d. 
k.  k.  g.  E.  Anstcdt.,  1865,  pp.  71,  163,  183,  and  1870,  p.  19. 


THE   GENESIS   OF   ORE-DEPOSITS.  89 

Mining  was  then  active  chiefly  on  the  north  slope  of  the  Benyes 
divide;  and  the  sedimentary  rocks  were  cut  off  towards  the  south 
by  andesite.  I  pointed  out  that  on  the  south  slope,  beyond  the 
andesite,  there  were  various  ancient  mines,  and  recommended  that 
they  be  explored  in  depth,  by  means  of  an  adit.  This  led  to  the 
discovery  of  several  deposits,  which  gave  new  life  to  the  industry. 
After  cutting  through  the  andesite,  the  explorers  found  steep  depos- 
its at  the  contact  of  andesite  and  limestone,  and,  in  the  limestone, 
near  its  contact  with  the  mica-slate,  a  flat  deposit,  which,  being 
above  the  ground-water  level,  had  been  transformed  into  carbonate 
of  lead. 

The  somewhat  complicated  conditions  are  shown  in  Fig.  70,  as  far 
as  this  can  be  done  in  a  single  section.  The  deposit  at  the  contact 
of  andesite  and  limestone  indicates  at  once  a  genetic  connection  with 
the  eruptive  rock,  and  renders  it  probable  that  the  ore-beds  also  are 
due  to  the  after-effects  of  the  eruption.  Even  on  the  north  slope 
there  were  some  reasons  for  this  conclusion.  For  instance,  at  the 
ore-bodies  locally  called  Thonstrassen,  ores  occurred  in  the  midst  of 
eruptive  breccia,  which  could  not  be  taken  for  fragments  of  the 
original  bed.  Baron  Constantine  von  Beust  *  found  traces  of 
"ring-ores,"  indicating  a  formation  in  open  cavities. 

In  seeking  an  explanation  of  all  the  facts,  I  was  led  to  give  up 
the  view  of  J.  Grimm,  f  which  he,  however,  still  maintained,  citing 
Offenbanya  as  another  instance  in  which  a  pre-existing  deposit  on 
the  contact  between  limestone  and  mica-slate,  had  been  shattered  by 
an  andesite-eruption.  But  in  that  instance,  also,  I  had  the  oppor- 
tunity to  satisfy  myself  that  the  then  accessible  mine-workings 
showed  no  fragments  of  an  earlier  ore-deposit,  but  only  ore-forma- 
tions under  the  influence  of  the  andesite. 

Grimm  had  had  in  mind  the  deposits  of  Rodna  and  Offenbanya 
when  he  established,  under  the  first  division  in  his  systematic  classi- 
fication, J  the  second  sub-division,  "  Occurrences  of  Ores  as  Frag- 
ments of  Earlier  Deposits,  in  Breccias,"  etc. 

Offenbdnya. — Offenbanya,  in  the  Transylvania  gold  district,  has 
various  deposits  analogous  to  those  of  Rodna,  and  also  veins,  with 

*  "  Bemerkungen  iiber  d.  Erzvorkommen  von  Rodna,"  Verh.  d.  k.  k.  geol.  JR.  A.t 
1869,  p.  367. 

f  J.  Grimm,  "Znr  Kenntniss  der  Erzvorkommen  von  Rodna,"  Verh.  d.  k.  k.  geol. 
R.  A.,  1869,  p.  367  ;  and  F.  Posepny,  "  Die  Natur  der  Erzlagerstatten  von  Rodna," 
ibid.,  1870,  p.  19. 

t  Die  Lagerstdtten  der  nutzbaren  Mineralien,  Prague,  1869,  p.  32. 


90  THE   GENESIS   OF   ORE-DEPOSITS. 

telluride  ores.  We  are  here  interested  in  its  mass-deposits,  at  the 
contact  of  limestone  and  andesite,  one  of  which  is  illustrated  in 
Fig.  71. 

Beneath  the  limestone  widely  extending  through  the  district, 
mining  has  disclosed  a  mica-slate  (the  so-called  underground  slate) ; 
and  at  the  contact  of  the  two  a  flat,  pyritous  deposit.  The  whole 
stratified  series  is  traversed  by  andesite;  but  near  its  contact  with 
the  limestone  a  steep,  rich  mass-deposit  extends  from  the  surface 
down  to  the  mica-slate.  This  deposit  is  highly  crustified,  and  was 
evidently  formed  in  a  pre-existing  space. 

The  flat  deposit  shows  no  crustification,  and  may  have  been  formed 
by  metasomatic  replacement  of  the  lime  at  the  contact  between  the 
impermeable  and  the  soluble  rock.  The  analogy  with  the  conditions 
on  the  south  slope  of  the  Benyes  mine,  at  Rodna,  is  evident,  though 
I  do  not  know  whether  at  Rodna  the  flat  deposit  has  been  followed 
as  yet  to  its  junction  with  the  steep  one.  * 

Rezbdnya. — Rezbanya  in  S.  E.  Hungary  represents  different  con- 
ditions. Here,  in  an  indistinctly  stratified  Mesozoic  limestone,  occur 
long  spaces  filled  with  ore,  descending  steeply  and  irregularly  in 
shape  like  that  of  the  cavity  produced  by  pouring  a  stream  of  warm 
water  upon  a  snow-bank.  This  extreme  case  is  of  great  theoretical 
interest,  although  such  ore-bodies  having  but  one  considerable  di- 
mension, and  that  in  the  most  unfavorable  direction  for  mining, 
mainly  downward,  are  not  attractive  from  a  commercial  standpoint. 
I  visited  Rezbanya  first  in  1868,  and  published  some  observations 
concerning  it,  which  may  have  contributed  to  induce  the  Hungarian 
government  to  take  up  the  subject  later,  and  intrust  to  me  a  more 
thorough  investigation.  I  will  here  mention  only  some  things,  in- 
teresting from  the  genetic  standpoint,  and  refer  for  details  to  my 
published  monograph  upon  the  subject.f 

In  the  Rezbanya  region,  lying  above  clay  slates  and  Permian 
and  Liassic  sandstones,  appear  numerous  isolated  bodies  of  lime- 
stone, indicated  by  their  fossils  to  be  of  various  ages,  from  the  Lias 
to  the  Neocomian,  seldom  distinctly  stratified,  and,  when  they  are 
traversed  by  eruptive  rocks,  often  showing  a  crystalline  structure. 


*  At  the  time  of  the  visit  of  G.  vom  Rath,  in  1878  (described  by  him  in  the  Zeit- 
schr.  d.  d.  geol.  Gesellsch.,  xxx.,  1878,  p.  556),  this  ore-body,  28  meters  (92  feet)  thick, 
had  been  developed  for  a  height  of  85  meters  (280  feel)  and  a  length  of  120  meters 
(394  feet)  without  reaching  its  termination. 

f  Geologuch-montanistische  Studie  der  Erzlagerst'dtten  von  Rezbanya,  Budapest,  1874. 


THE   GENESIS   OF   ORE-DEPOSITS.  91 

The  ore-filling  is  mostly  confined  to  the  neighborhood  of  the  erupt- 
ives,  and  sometimes  to  the  contact,  where  garnet-rock  occurs  as  a 
well-known  product  of  local  metamorphosis.  Since  my  examination, 
there  may  have  been,  in  this  region,  many  interesting  and  scientif- 
ically important  developments,  which  are  unfortunately  unknown  to 
me.  On  the  basis  of  my  old  notes  only,  I  shall  confine  myself  to 
the  description  of  a  single  district,  cut  off  from  commercial  communi- 
cation, that  of  Yalle  Sacca.  The  name  is  that  of  the  valley,  which 
heads  in  a  high  mountain  range  of  Permian  and  Liassic  sandstones, 
and  after  a  short  course  ends  in  a  wild  limestone  caflon,  leading 
into  the  Galbina  valley.  The  sides  of  Valle  Sacca  consist  chiefly 
of  limestone,  which  is  traversed  by  a  number  of  eruptive  dikes  and 
one  larger  mass  of  a  syenitic  character.  Fig.  64  gives  a  somewhat 
generalized  section  of  the  NW.  slope  of  the  valley  and  district  on 
the  line  of  the  so-called  fourth  adit.  At  the  adit-mouth  is  cut  the 
syenite  mass,  which  extends  also  to  the  opposite  slope ;  and  the  ad- 
joining portion  of  the  limestone  has  been  metamorphosed  to  a  crys- 
talline mass,  while  the  limestone  further  SW.  is  for  the  most  part 
still  compact.  On  the  west  side,  the  limestone  adjoins  sandstone 
along  a  N.— S.  line,  which  doubtless  represents  a  large  fault.  Ap- 
proximately parallel  to  it  run  the  greenstone  dikes,  which,  though 
they  seem  to  be  mutually  parallel,  in  reality  intersect  one  another  at 
very  acute  angles,  thus  constituting  a  highly  elongated  net-work. 
The  dikes  are  not  alike.  Most  of  them  may  be  considered  aphan- 
itic  or  dioritic;  one,  however,  is  quartz-porphyry,  with  dihexahedra 
of  quartz,  of  pea-size. 

The  principal  deposit  is  the  so-called  Reichenstein  stock,  which 
had  been  worked,  during  the  period  prior  to  my  visit,  to  a  depth  of 
about  400  meters  (1300  feet),  from  its  outcrop,  310  meters  above  the 
deepest  adit,  to  a  level  60  meters  below  the  adit.  Fig.  65  shows  the 
form  of  the  ore-channel  on  the  strike.  The  horizontal  section  of 
the  body  was  most  frequently  circular  or  elliptical.  In  some  places 
one  dimension  strongly  predominated,  so  as  to  give  the  appearance 
of  a  fissure-filling.  At  the  outcrop,  according  to  the  old  maps,  there 
was  but  one  channel.  Below,  this  divided  into  neighboring  and 
mutually  connected  branches.  Several  of  these  might  continue  par- 
allel and  independent  for  considerable  distances.  The  total  sectional 
area  of  these  channels  averaged  perhaps  20  to  30  square  meters  (215 
to  322  square  feet) ;  but  at  some  levels  the  deposit  was  only  present 
in  traces,  whereas  at  others  it  had  many  times  its  average  section. 
Fig.  66  shows,  by  the  difference  between  the  plumb-line  and  the 


92  THE   GENESIS  OF   ORE-DEPOSITS. 

arrow,  the  angle  between  the  true  dip  and  the  pitch  of  the  ore-body, 
oblique  to  it. 

The  ores  were  doubtless  sulphides  originally,  but  were  afterwards 
oxidized  in  places.  Rich  silver-ores  predominated,  especially  argen- 
tite,  pieces  of  which  weighing  several  pounds  appear  to  have  been 
no  rarity.  Besides  this  mineral  there  were  hessite  (telluride  of  sil- 
ver), tetrahedrite,  redruthite,  galena,  bismuthinite,  and  various  py- 
rites. Taking  these  together  with  the  oxidized  ores,  the  deposit  rep- 
resented a  whole  mineral  cabinet.  The  maximum  silver-value  was 
reported  as  12  to  20  kilos  per  1000  (1.2  to  2  per  cent),  the  gold 
being  3  grammes  to  each  kilo  of  silver.  The  percentage  of  lead  was 
about  twenty  times,  and  that  of  copper  about  ten  times,  as  great  as  of 
silver.  The  metric  ton  (2206  pounds)  would  yield,  at  this  rate,  24 
to  40  per  cent,  of  lead,  12  to  20  per  cent,  of  copper,  12  to  20  kilos 
(386  to  643  ounces  troy)  of  silver,  and  36  to  60  grammes  (1.15  to 
1.83  ounces  troy)  of  gold.  The  deposit  was  therefore  a  bonanza 
in  the  American  sense.  In  fact,  it  yielded  from  §100  to  $150  per 
ton. 

Although  I  could  not  see  this  deposit  in  process  of  extraction,  I 
was  able  to  conclude  positively,  from  specimens  of  the  ore  and  from 
the  analogy  of  similar  deposits  in  the  district,  that  it  had  been  formed 
by  the  precipitation  of  successive  crusts. 

As  regarded  the  origin  of  the  cavity,  I  was  at  first  influenced  in 
my  views  by  the  numerous  caves  of  the  region.  The  mines  re- 
peatedly reached  caves,  into  which  the  mine-water  could  be  dis- 
charged without  filling  them,  there  being  some  subterranean  outlet. 
But  these  caves,  as  I  have  explained  in  Part  I.,  were  formed  by  de- 
scending liquids  of  the  vadose  circulation ;  and  to  assume  a  similar 
origin  for  the  cavities  filled  by  the  ore-bodies  would  be  to  assume 
that  the  latter  cavities  were  formed  in  a  manner  directly  opposite  to 
that  in  which  they  were  filled — which  is  highly  improbable. 

It  was  not  until  later,  when  I  had  become  acquainted  with  the 
observations  of  J.  Noggerath  (cited  in  Part  I.)  on  the  thermal  springs 
of  Burtscheid,  that  I  recognized  that  ascending  mineral  springs  are 
able  to  cut  their  own  way  to  the  surface,  forming  the  channels  which 
they  ultimately  fill  with  ore.  The  most  difficult  feature  of  all, 
namely,  the  nearly  cylindrical  form  of  the  ore-bodies  of  Valle  Sacca, 
was  thus  satisfactorily  explained. 

The  channel  of  the  Reichenstein  body  runs  vertically  for  400 
meters  (1312  feet)  in  limestone  between  greenstone  dikes;  or,  in 
other  words,  in  a  zone  of  lime  between  two  zones  of  impermeable 


THE   GENESIS   OF   OHE-DEPOSITS.  93 

rock.  The  dikes  therefore  control  its  direction.  It  follows  down- 
ward nearly  at  the  angle  of  their  steepest  dip,  but  with  a  pitch  south- 
ward, giving  it  a  "  false  dip." 

The  sections  of  the  various  workings  show  that  the  ore-body  ap- 
parently ended  at  one  side  of  the  dike  and  recommenced  at  the  other 
side,  as  if  it  had  passed  through.  In  that  case,  porous  places  in  the 
dike-mass,  at  the  intersection,  will  have  determined  the  track  of  the 
channel.  It  is  significant  that  the  Reichenstein  ore-channel  passes 
in  depth  through  the  dikes  to  the  SW.,  towards  what  is  probably 
a  great  fault-fissure,  and  not  in  the  direction  of  the  present  drainage. 
Nor  could  the  former  deep  drainage  from  this  channel  have  been  to 
the  NE.,  along  the  contact  between  the  limestone  and  the  underly- 
ing Liassic  sandstone  (which,  in  fact,  appears  at  a  lower  level,  where 
the  Valle  Sacca  joins  the  Galbina  valley),  for  the  reason  that  all  the 
barriers  of  the  greenstone  dikes,  unquestionably  extending  from  the 
limestone  into  the  sandstone,  would  have  opposed  that  flow.  The 
stratigraphical  conditions  thus  exclude  the  possibility  that  this  chan- 
nel was  formed  by  vadose  circulation,  and  render  more  probable  the 
view  that  it  owes  its  origin  to  the  ascending  waters  of  the  deep  cir- 
culation, which  certainly  effected  the  filling  of  it. 

Raibl. — Raibl,  in  Carinthia,  is  the  best  representative  of  a  group 
of  deposits  which  were  at  a  recent  period  taken  to  be  genuine  beds 
even  by  V.  M.  Lipold,*  then  the  best  authority  on  the  mines  of  the 
Alps  in  general.  Here  and  there,  as,  for  instance,  by  A.  Morlot,f 
observations  were  made  which  threw  some  doubt  on  this  conception ; 
but  since  they  did  not  fit  into  the  prevailing  system,  they  remained 
disregarded.  It  was  my  fortune  to  establish  the  truth  of  the  situa- 
tion. Prof,  von  Groddeck  kindly  characterized  my  investigation  ot 
it  as  "  opening  a  new  path,"  and  adopted  the  filling  of  spaces  of  dis- 
solution as  a  class  in  his  system  (op.  eit.,  pp.  10,  236,  etc.). 

Such  deposits  occur  in  Carinthia,  in  an  E.-W.  limestone  alpine 
range,  of  which  Eaibl  is  the  western  end ;  and  also  somewhat  fur- 
ther north,  in  the  zone  of  Bleiberg  near  Yillach,  chiefly  in  a  lime- 
stone, early  denominated  for  this  reason  the  ore-bearing  limestone, 
and  more  recently  determined  as  Triassic. 

The  ores  occurred  mostly  in  the  vicinity  of  certain  intercalated 
slates,  which  seemed  always  to  occupy  the  same  "  Raibl  horizon," 
and  thus  led  to  the  conclusion  that  the  ore-deposits  (naturally 
believed  to  be  of  contemporaneous  origin)  likewise  occupied  a  fixed 

*  Jahrb.  d.  k.  L  g.  E.  Amt.,  1862,  Verh.,  p.  292. 
f  Ibid.,  1850,  i.,  p.  266. 


94  THE   GENESIS   OF   ORE-DEPOSITS. 

horizon.  But  it  soon  appeared  that  the  slate  at  Bleiberg  belonged 
to  a  somewhat  different  horizon  in  the  Trias;  and  I  ventured  to 
assert  that  the  impermeability  of  the  slates,  as  compared  with  the 
solubility  of  the  limestone,  had  had  something  to  do  with  the  ore- 
deposition,  which  was  a  secondary  formation  in  the  rocks. 

There  are  found  at  Raibl,  some  distance  below  the  slates,  in  the 
limestone  which  conformably  underlies  them,  what  seern  indeed  at 
first  glance  to  be  beds  of  ore.  They  consist  chiefly  of  a  coarsely 
crystalline  galena,  with  pyrites,  and  a  zincblende  (wurtzite)  in  very 
thin  crusts,  hence  called  Schaienblende.  A  closer  study,  however, 
of  the  extremely  distinct  crustification  reveals  that  it  does  not  repre- 
sent the  stratification,  which,  on  the  contrary,  it  crosses  at  all  angles, 
being  in  fact  the  filling  of  irregular  spaces,  traversing  the  limestone 
in  every  direction. 

Further  light  is  furnished  by  the  seams  which  here  occur.  As  is 
generally  the  case  in  limestone,  these  are  rarely  wide  fissures,  but 
usually  mere  partings  between  two  polished  walls  in  close  contact. 
Slickensides,  etc.,  identify  them  at  once  as  results  of  friction,  caused 
by  the  forcible  rubbing  together  of  walls  perhaps  originally  irregu- 
lar. The  plane  of  contact  with  the  slates  offers  a  means  of  deter- 
mining the  extent  of  the  movement  along  some  of  these  insignificant- 
looking  seams;  and  it  appears  that  dislocations  as  great  as  40  to  60 
meters  (131  to  196  feet)  have  thus  taken  place.  Since  the  slates 
possess  some  flexibility,  they  were  sharply  bent  in  the  immediate 
neighborhood  of  the  fault,  a  feature  which,  on  account  of  its  theo- 
retical importance,  I  have  illustrated  in  Fig.  69. 

In  the  seams  themselves  (locally  called  Blatter  or  "leaves'')  there 
can  be,  of  course,  no  deposit  of  ore  ;  but  such  deposition  occurs  out- 
side of  the  fissure,  when  soluble  rocks  like  this  limestone  are  trav- 
ersed. Geode-spaces  were  thus  leached  out,  and  are  found  filled 
with  distinct  mineral  crusts,  as  is  shown  in  Fig.  72,  representing 
the  face  of  a  level  on  the  so-called  Johanniblatt. 

It  cannot  be  doubted  that  the  ore-supply  came  from  the  seams ; 
and  when  we  find  such  seams  also  in  large  and  rich  deposits  of  simi- 
lar character,  like  those  on  the  north  slope  of  the  Konigsberg  at 
Raibl,  we  must  concede  to  them  a  similar  significance  as  regards  the 
ore-deposition. 

To  the  more  important  of  these  seams,  J.  Waldauf  von  Walden- 
stein*  and  Dr.  W.  Fuchsf  had  already  called  attention.  These  are 

*  Die  besonderen  Lagerstatten  d.  nutzb.  Minercdien,    Vienna,  1824,    Plate    III., 
Fig.  4. 
f  Beitrdge  zur  Lehre  von  den  Erzlagerqtatten,  Vienna,  1846,  Plate  I.,  p.  23. 


THE   GENESIS   OF   ORE-DEPOSITS.  95 

the  Morgen,  Abend,  Johann  and  Josef.  The  first  three  meet  at  an 
angle  of  about  30°,  and  form  the  boundaries  of  ore-bodies,  extend- 
ing downwards  along  the  seams  with  a  horizontal  length  of  40  to  80 
meters  (131  to  262  feet)  and  a  total  thickness  (including  portions  too 
poor  to  work)  of  10  to  50  meters  (38  to  164  feet).  Many  of  the 
mine-managers  believed  that  there  was  here  a  continuous  ore-bed 
which  had  been  faulted  into  separate  bodies  by  the  seams,  and  nu- 
merous exploring  levels  were  undertaken  to  develop  this  assumed 
bed,  but  all  in  vain.  Nothing  was  found,  except  a  few  more  or  less 
independent  ore-shoots  on  one  or  both  sides  of  the  seams,  similar  to 
those  which  have  been  encountered  in  recent  years  at  Leadville. 

The  foregoing  observations  will  facilitate  a  comprehension  of  Figs. 
67  and  68,  the  former  showing  a  section  (not  strictly  in  one  plane) 
of  the  ore-shoots  in  the  government  mine,  and  the  latter  a  similar 
picture  of  the  Struggl  private  mine.  In  the  former,  separate  ore- 
bodies  are  observed  to  the  distance  of  500  meters  (1640  feet)  above 
the  bottom  of  the  valley,  and  in  1870  the  continuous  ore-shoots  ex- 
tended from  425  meters  (1394  feet)  above  to  150  meters  (492  feet) 
below  that  level,  a  total  vertical  height  of  575  meters  (1886  feet). 

It  will  be  seen  that  the  several  portions  of  the  slopes  descend 
more  or  less  parallel  with  the  stratification  and  the  lime-slate  con- 
tact, but  with  steps  or  offsets.  The  highest  portion  of  the  Abend- 
blatt  ore-shoot  is  about  300  meters  (984  feet)  in  the  foot- wall  of  the 
slate-contact;  at  greater  depths  there  are  portions  130,  150,  85 
and  finally  10  meters  only  (426,  492,  279  and  33  feet)  from  that 
plane. 

It  thus  appears  that  the  ore-sh*oots  are  approaching  the  contact  in 
depth,  and  will  probably  follow  it  below.  It  is,  therefore,  not  here 
the  case  that  a  particular  layer  in  the  limestone  has  favored  the 
formation  of  spaces  of  dissolution.  If  that  were  true,  the  ore-body, 
notwithstanding  the  convergence  of  the  seams  southward,  should 
maintain  a  more  or  less  uniform  distance  from  the  contact,  which  it 
does  not  do,  either  in  the  section  of  Fig.  67  or  in  that  of  the  Struggl 
mine,  Fig.  68,  where  the  opposite  occurs,  namely,  the  ore-shoots  depart 
from  the  contact  in  depth.  I  must  confess  myself  unable  to  explain 
these  variations  in  the  Eaibl  ore-shoots  with  the  light  afforded  by  the 
mine-workings  down  to  1870.  But  I  am  convinced  that  the  ex- 
planation will  be  found  by  further  thorough  study.  Meanwhile,  I 
can  only  claim  the  credit  of  having  placed  the  inquiry  upon  what  I 
deem  to  be  the  true  road,  and  express  my  regret  that  in  the  twenty 
years  since  the  publication  of  my  monograph  on  the  Raibl  deposits 


96  THE   GENESIS   OF   ORE-DEPOSITS. 

no  further  progress  seems  to  have  been  made  in  the  interpretation  of 
the  very  numerous  analogous  ore-deposits. 

The  North  of  England. — I  cannot  omit  to  mention  here  the  region, 
classic  in  this  respect,  of  the  North  of  England.  Lead-mining  is 
actively  carried  on  in  the  carboniferous  limestone  of  Northumber- 
land, Durham,  Cumberland  and  Westmoreland,  where  the  lime- 
stone alternates  with  sandstone  and  slate  and  occasional  intercalated 
eruptives  or  their  tufas.  This  formation  is  traversed  and  faulted  by 
a  variety  of  seams  and  veins;  and  the  veins  are  generally  richer 
where  they  are  in  the  limestone.  The  thinner  and  more  extensively 
faulted  of  the  limestone  strata  are  entirely,  severed,  so  that  they  ap- 
pear in  different  horizons  on  opposite  sides  of  the  faulting-fissure. 
Where  they  are  thicker  or  less  widely  thrown  by  the  fault,  however, 
limestone  appears  on  both  sides  of  the  latter.  It  is  obvious  that  an 
accurate  picture  of  these  conditions  would  furnish  valuable  data  con- 
cerning the  ore-genesis. 

The  several  descriptions  of  the  mines  do  not  specify  whether  the 
ore  of  such  veins  as  become  rich  in  the  limestone  occurs  in  the  fis- 
sures proper  or  outside  of  them  in  spaces  of  dissolution  in  the  lime- 
stone. The  latter  is  clearly  the  case  in  the  so-called  "flats."  In 
certain  horizons,  where  the  seams  encounter  the  soluble  lime-stratum, 
the  ore-filling  departs  from  the  fissure  into  the  geodes  of  the  rock, 
forming  frequently  very  rich  ore-bodies  of  highly  irregular  form, 
but  flat,  by  reason  of  their  following  the  soluble  stratum.  The  ore- 
filling  continues  to  a  very  uncertain  distance  from  the  fracture-plane, 
and  is  generally  accompanied  with  frequent  cavities,  the  walls  of 
which  are  covered  with  crusts  of  calcite,  blende  and  galena.  Empty 
caverns  also  occur.*  We  cannot  but  recognize  immediately  in  this 
description  the  type  as  to  character  and  position  of  the  Raibl  de- 
posits, the  druses  of  which  are  here  represented  by  the  incrusted 
cavities.  The  empty  caverns  have  doubtless  been  formed  by  subse- 
quent processes  of  dissolution. 

These  phenomena  occur  in  the  North  of  England  on  a  very  large 
scale.  Veins  are  mentioned  which  have  been  traced  for  several 
miles,  and  the  connected  subterranean  channels  of  dissolution  must 
be  also  of  considerable  length.  The  existence  of  laterally  extensive 
ore-channels,  and  hence  of  an  underground  circulation  of  mineral 


*  See  J.  A.  Phillips,  Ore-Deposits,  p.  180;  also,  D.  C.  Davies,  Metalliferous  Min- 
erals and  Mining,  London,  1880,  p.  216 ;  and  the  works  of  W.  Wallace,  T.  Sopwith, 
Westgarth  Foster,  C.  E.  De  Ranee,  R.  Hunt,  etc. 


THE   GENESIS   OF   ORE-DEPOSITS.  97 

waters  not  formerly  suspected  is  thus  revealed,  and  an  entirely  new 
light  is  thrown  upon  the  so-called  "  ore-beds." 

These  observations  are  confirmed  in  another  quarter  by  develop- 
ments in  Western  North  America,  where  very  numerous  ore-deposits 
are  connected  with  limestone.  It  is  impossible  to  bring  forward 
here  the  whole  of  this  material.  I  must  limit  myself  to  certain 
localities,  which  have  been  thoroughly  studied  and  described  in  pub- 
lications. 

Leadville. — I  will  begin  with  Leadville,  the  recent  blossom  of  the 
mountain-world  of  Colorado.  I  am,  indeed,  not  personally  ac- 
quainted with  this  locality,  the  importance  of  which  was  not  recog- 
nized until  after  my  visit  to  the  United  States  ;  but  my  lively  in- 
terest in  it  is  testified  by  the  article  concerning  it,  which  I  laboriously 
compiled  in  1879  from  the  incomplete  data  then  available.*  Later, 
when  S.  F.  Emmons  had  finished  his  surveys,  but  before  the  publi- 
cation of  his  epoch-making  work,f  I  had  opportunity  to  exchange 
views  with  him  concerning  the  genetic  condition,  and  to  confess  that 
I  was  unable  to  share  his  opinion  as  to  the  downward  course  of  the 
mineralizing  solutions — an  opinion  which  was  opposed  to  the  then 
prevalent  belief.  The  mine-workings  have  been  greatly  extended 
since  that  time,  and  Emmons's  suggestion  has  been  shown  by  several 
mining  engineers,;);  on  the  basis  of  thorough  studies  underground, 
to  be  untenable;  so  that  the  Leadville  deposits  appear,  as  regards 
the  origin  of  their  metallic  contents,  to  form  no  exception  to  the 
history  of  other  similar  deposits.  I  think  Emmons  himself  must 
have  acknowledged  the  force  of  these  criticisms,  which  do  not  detract 
in  the  least  from  the  merit  of  his  accurate  investigation  of  the 
district. 

On  the  west  slope  of  the  Mosquito  range  appears  a  series  of  un- 
dulating Palaeozoic  strata,  with  heavy  layers  and  intrusive  masses 
of  eruptive  rocks,  and  traversed  by  numerous  faults.  This  forma- 
tion covers  a  large  area,  only  a  comparatively  small  portion  of  which, 
namely,  the  vicinity  of  Leadville,  is  ore-bearing, — a  circumstance 
which  of  itself  points  to  a  local  origin  for  the  ore.  As  is  well- 

*  "Leadville,  die  neue  Bleistadt  in  Colorado."—  Oesterr.  Zeitsch.,  1879. 

f  "Geology  and  Mining  Industry  of  Leadville." — U.S.  Oeol.  Survey,  Monogr. 
xii.,  Washington,  1886. 

J  F.  T.  Freeland,  "  The  Sulphide-Deposits  of  South  Iron  Hill."— Trans.  A.  I. 
M.E.,  1885,  xiv.,  181;  C.  M.  Kolker,  "The  Leadville  Ore- Deposits."— Ibid.,  p. 
273;  A.  A.  Blow,  "The  Geology  and  Ore-Deposits  of  Iron  Hill."— Ibid.,  1889, 
xviii.,  145. 

7 


98  THE   GENESIS   OF   ORE-DEPOSITS. 

known,  the  series  of  rocks  has  the  following  order  downwards: 
white  porphyry,  blue  limestone,  gray  porphyry,  white  limestone, 
lower  quartzite, — which  I  will  denote,  for  brevity,  by  their  initial 
letters.  The  ore-deposits  occur  chiefly  at  the  contact  between  the 
first  two  members  of  the  series,  below  the  WP.  and  above  the  BL. 
In  the  upper  levels  they  are  oxidized  and  chloridized  (doubt- 
less in  this,  as  in  other  places,  through  the  action  of  descending 
ground-water)  ;  in  lower  levels  they  appear  in  their  original  form  as 
sulphides.  That  this  was  the  condition  in  which  they  were  origin- 
ally precipitated,  Emmons  admits;  only  their  position  seems  to  him 
to  exclude  the  hypothesis  of  ascending  solutions.  He  says  (op.  rit.,  p. 
573). 

l<  The  principal  water-channel  at  the  time  of  deposition  was  evidently  the  upper 
contact  of  the  blue  limestone  with  an  overlying  porphyry;  and  from  this  surface 
they  penetrated  downwards  into  the  mass  of  the  limestone.  It  may  be  assumed, 
therefore,  that  the  currents  were  descending  under  the  influence  of  gravity,  rather 
than  ascendiug  under  the  influence  of  heat." 

But  he  omits  to  explain  how  he  conceives  it  possible  that  mineral 
solutions  descending  by  gravity,  and  hence  certainly  having  been 
in  contact  with  the  surface-region,  could  deposit  sulphides.  Assum- 
ing such  an  explanation  to  be  furnished  by  reduction  through 
organic  substances,  the  question  arises  whither  such  descending 
currents  could  go.  Here  the  theory  is  in  conflict  with  our  concep- 
tion of  the  underground  circulations. 

As  A.  A.  Blow  has  shown,  however,  a  leaching  of  the  WP.  can- 
not by  any  means  have  supplied  the  ore ;  for  this  rock  is  not  at  all 
decomposed,  as  in  that  case  it  must  have  been.  On  the  other  hand, 
there  are  found  in  the  intrusive  beds  and  dikes  of  the  lower  GP. 
various  indications  that  this  rock  had  more  to  do  with  the  ore- 
deposition.  Along  these  dikes  lie  the  ore-shoots, — in  other  words, 
the  channels  in  which  ore  was  deposited. 

It  was  at  first  tacitly  assumed  that  the  ore  occupied  the  whole 
plane  of  the  contact,  although  it  was  known  that  the  richest  bodies 
occupied  particular  zones  in  this  plane.  The  importance  of  these 
ore-shoots  was  recognized  later  ;  and  we  may  now  consider  the 
Leadville  occurrence  as  presenting,  not  a  single  contact-deposit  or 
ore-bed,  but  a  complex  group  of  ore-shoots,  such  as  we  have  ob- 
served in  other  ore-deposits  in  limestone.  These  ore-shoots  lie,  in 
Leadville,  at  the  contact  between  the  soluble  and  the  eruptive  rock  ; 
while  in  Raibl  they  appear  near  the  contact  of  two  stratified  rocks, 
one  soluble  and  the  other  impermeable.  The  physical  process 


THE   GENESIS   OF   ORE-DEPOSITS.  99 

forming  these  ore-shoots  was  doubtless  the  same  in  both  cases.  The 
mineral  solutions,  ascending  under  pressure,  and  seeking  a  path  to 
the  surface,  followed,  as  some  would  say,  the  line  of  the  least  resist- 
ance; or,  as  I  would  prefer  to  express  it,  there  was  established  in 
the  soluble  rock  a  line  of  maximum  circulation,  resulting  in  the 
dissolving-out  of  a  channel. 

Such  dissolution,  however,  occurred  not  only  on  the  contact  be- 
tween WP.  and  BL.,  but  also  at  other  contacts.  Thus  L.  D. 
Ricketts  (Rolker,  I.  c.,  p.  284)  gives  a  section  of  a  mine  on  Carbon- 
ate Hill,  showing  a  second,  deeper  ore-horizon  between  the  GP. 
(dike  porphyry)  and  the  underlying  limestone.  According  to  Rol- 
ker, the  BL.  of  Fryer  Hill  was  relativejy  thin,  and  has  been  re- 
placed with  ore  and  accompanying  minerals,  all  but  small  remnants 
of  dolomitic  sand.  These  are  generally  above  the  ore,  i.e.,  along 
the  upper  contact,  whereas,  according  to  Emmons's  theory,  they 
should  be  replaced  with  ore. 

The  sections  given  by  F.  T.  Freeland  (L  c.,  Figs.  1  and  6)  show 
two  ore-horizons,  the  thicker  of  which  is  below  the  W.  P.,  and  the 
other  below  an  intrusion  of  G.  P. ;  and  Mr.  Blow's  sections  from 
Iron  Hill  reveal  similar  phenomena  (see  Fig.  73,  a  section  through 
the  McKean  shaft).  The  ore-shoots  are,  of  course,  irregular  in 
form  ;  but  a  main  general  direction  can  be  recognized,  which  is 
eastward  in  Fryer  Hill,  but  northeastward  in  Carbonate  and  Iron 
Hill,  representing  the  course  of  the  channel  through  which  the 
mineral  solutions  circulated. 

In  the  data  at  hand  concerning  the  structure  of  the  deposits, 
nothing  is  said  of  a  distinct  crustification.  It  is  to  be  remembered, 
of  course,  that  mining  operations  hitherto  have  been  largely  confined 
to  the  upper  and  decomposed  zone,  whereas  this  phenomenon,  if 
ever  so  fully  developed,  would  show  itself  clearly  only  in  the  unde- 
composed  zone.  When  we  read,  however,  of  great  "  horses "  of 
country-rock,  encountered  in  the  midst  of  the  ore,  we  must  believe 
that  the  deposit  is  due  not  so  much  to  a  rnetasomatic  replacement  of 
the  limestone  as  to  the  filling  of  spaces  of  dissolution ;  and  hence  it 
should  exhibit  the  characteristic  sign  of  such  a  filling,  namely,  crus- 
tification. It  seems  to  me  that  this  point  has  not  received  the  at- 
tention it  deserves;  and  I  hope  that  observations  in  the  undecom- 
posed  ore-zones  will  give  more  definite  data  as  to  structure.  It  is 
difficult  to  believe  that  metasomatic  processes  could  produce  such 
pronounced  ore-shoots  as  those  described  at  Leadville. 

Impressed  by  Emmons's  views,  and  long  before  the  connection 


100  THE   GENESIS   OF   ORE-DEPOSITS. 

of  the  ore-deposition  with  the  GP.  of  the  dykes  had  been  shown, 
I  wondered,  at  one  time,  whether  the  ore  might  not  have  come  some- 
how from  the  fault-fissures  into  the  contact-channels.  But  Mr. 
Emmons  pointed  out  to  me  that  the  faults  contain  only  ore  which 
has  been  dragged  in  from  the  pre-existing  bodies,  the  formation  of 
which  was  complete  before  the  faulting  took  place. 

Conditions  analogous  to  those  of  Leadville  are  exhibited  in  most 
of  the  ore-deposits  in  limestone  occurring  in  the  American  West. 
But,  with  few  exceptions,  we  have  only  hasty  descriptions  of  them, 
and  sometimes  nothing  more  than  business  "  puffs." 

Red  Mountain. — A  remarkable  occurrence  has  been  described  in 
the  Red  Mountain  district,  Ouray  County,  Colorado.*  In  the  midst 
of  the  deposits  of  the  San  Juan  region,  which  are  connected  with 
eruptive  rocks,  appears  a  body  of  Mesozoic  strata,  carrying,  at  the 
contact  of  a  quartzite  with  the  underlying  limestone,  a  deposit  of 
the  sulphides  of  iron,  lead,  copper,  silver,  and  the  products  of  their 
decomposition,  rich  in  silver  and  somewhat  auriferous  (2110  to  3980 
grammes  of  silver  and  3  to  6  gram  rues  of  gold  per  metric  ton,  or 
59  to  111  ounces  of  silver  and  0.08  to  0.17  ounce  of  gold  per  ton  of 
2000  pounds).  At  certain  points  the  ores  extend  far  down  into  the 
limestone,  and  in  the  section  shown  in  Fig.  74  the  ore  follows  a 
fault-fissure  through  the  whole  thickness  of  the  limestone  into  a 
second  quartzite  stratum  below.  The  stratified  formation  is  mostly 
covered  with  andesite,  in  which  occur  ore- bearing  veins  in  fissure- 
form. 

In  the  neighborhood,  at  Mineral  Farm,  another  contact-deposit 
between  limestone  and  quartzite  is  known,  consisting  of  barite  with 
argentiferous  galena  and  tetrahedrite.  Both  the  above  deposits  are 
but  briefly  described,  and  perhaps  have  not  been  extensively  worked. 
Their  conditions  of  position  and  the  predominance  of  lead  and 
•silver-ores  strangly  remind  one  of  Leadville. 

In  the  adjacent  Territories  of  New  Mexico  and  Arizona,  various 
copper-deposits  occur  in  limestone,  and  at  its  contact  with  eruptive 
rocks  ;  as,  for  instance  (according  to  the  outline-description  of  A.  F. 
Wendtf),  in  the  Clifton  and  Bisbee  districts.  The  sections  accom- 
panying Mr.  Wendt's  paper  remind  me  of  some  of  the  deposits 
described  in  my  monograph,  at  Rezbanya,  at  M&lnorudjansk,  and 
at  Bogoslavsk  in  the  Ural.  Fig.  75  is  an  interesting  section  from 

*  G.  E.  Kedzie,  "  The  Bedded  Ore-Deposits  of  Red  Mountain  District,"  Trans. 
A.  I.  M.  E.,  1886,  xvi.,  570. 
f  "The  Copper-Ores  of  the  Southwest,"  Trans.  A.  1.  M.  E.,  1886,  xv.,  25. 


THE   GENESIS   OF   ORE-DEPOSITS.  10't  ' 

the  Clifton  district,  in  Arizona,  showing  two  steep  ore-shoots,  paral- 
lel with  the  felsite  dike,  and  a  flat  one,  parallel  with  the  bedding. 

Utah. — With  respect  to  Utah,  the  paper  of  0.  J.  Hollister*  gives 
a  general  survey  of  the  deposits  of  the  Territory,  and  mentions  a 
number  which  occur  in  limestone.  Some  of  those  in  central  Utah  I 
have  had  the  opportunity  to  see  personally,  during  the  period  when 
mining  was  still  confined  chiefly  to  the  decomposed  upper  levels.  I 
refer  to  the  Prince  of  Wales  and  the  Reed  and  Benson,  in  Big  Cot- 
tonwood ;  the  Emma  and  the  Flagstaff,  in  Little  Cottonwood ;  the 
Old  Telegraph,  in  West  Mountain,  and  the  Hidden  Treasure,  in 
Dry  Cafion  district. 

Paleozoic  strata  are  here  traversed  by  frequent  eruptive  dikes,  and 
by  two  intersecting  systems  of  faults.  The  ore-deposits,  of  varying 
thickness,  in  the  limestone  have,  as  a  rule,  the  form  of  "  chimneys, " 
either  lying  flat,  with  the  bedding,  or  standing  steeply  along  the 
dikes  and  faults.  This  gave  rise  in  the  beginning  (when  the  na- 
ture of  the  deposits  was  not  understood,  and  the  conception  of  a  typi- 
cal "lode"  generally  prevailed)  to  a  series  of  disappointments  and 
mistakes  in  mining,  of  which  the  history  of  the  Emma  mine  fur- 
nishes an  interesting  example.  Apparently  the  irregularity  and  the 
complications  of  these  deposits  came  to  be  better  known  afterwards 

The  (sometimes  very  rich)  ores  consist  chiefly  of  sulphides  of 
lead  and  silver,  and  the  products  of  their  decomposition.  In  some 
cases  (e.g.,  Hidden  Treasure)  cuprite  occurs,  with  native  copper; 
and  in  the  Camp  Floyd  district  cinnabar  also  is  found. 

Nevada. — In  Nevada,  adjoining  Utah  on  the  west,  deposits  of  this 
class  are  likewise  abundantly  represented.  I  will  mention  only  the 
two  districts  which  have  been  most  thoroughly  studied,  namely, 
White  Pine  and  Eureka. 

With  regard  to  the  former,  the  work  of  Arnold  Hague  (1870)t, 
demonstrating  the  peculiar  character  of  the  White  Pine  deposits,  led 
me  to  seek  for  European  analogues. J  I  found  that,  apart  from  the 
condition  of  the  ores,  which  at  White  Pine  are  found  in  the  oxidized 
and  chloridized  zone,  there  was  an  analogy  with  all  the  European 
ore-deposits  in  limestone,  but  especially  with  the  conditions  at 
Raibl. 

*  "Gold- and  Silver-Mining  in  Utah,"  Trans.  A.  I.  M.  E.,  1887,  xvi.,  3. 

f  "Geology  of  the  White  Pine  District,"  U.  S.  Geol.  Surv.  of  the  40*A  Parallel, 
vol.  iii,  Mining  Industry,  p.  409. 

J  F.  Posepny,  "Das  Erzvorkommen  vom  White  Pine  District,  u.  dessen  euro- 
paische  Analogien,"  Verh.  d.  k.  k.  g.  R.  A.  1872,  p.  186. 


103  THE   GENESIS   OF   ORE-DEPOSITS. 

Devonian  limestones  and  calcareous  slates  are  overlain  at  White 
Pine  by  Carboniferous  clay-slates,  sandstones  and  limestones  ;  and 
the  ores  occur  only  in  Devonian  limestone  and  at  its  contact  with 
the  calcareous  slates  on  a  N.  and  S.  anticlinal.  The  ores  and  the  as- 
sociated minerals  (quartz,  calcite,  gypsum,  fluorspar,  barite,  rhodon- 
ite, rhodochrosite,  with  the  chlorides,  bromides,  oxides,  and  car- 
bonates of  various  metals,  especially  silver,  lead  and  copper)  fill  the 
cavities  in  the  limestone  and  surround  its  fragments. 

The  various  mines  represent  different  stages  in  one  and  the  same 
process.  In  the  Eberhardt,  two  fissures  crossing  the  anticlinal 
bound  the  ore-body  (like  the  MorgenUatt  and  the  Abendblatt  at 
Raibl.)  This  consists  of  a  lime-breccia  (Kalktyphon),  the  frag- 
ments of  which  fit  together,  and  are  cemented  by  ore-bearing  quartz 
seamc.  The  Hidden  Treasure  mine  contained  the  ore  in  geodes, 
at  the  contact  of  the  limestone  and  slate.  In  the  Aurora,  the  ore 
was  in  bodies  stretching  N.  and  S.  In  Bromide,  Chloride  and  Po- 
gonip  Flats,  the  ores  occurred  in  geodes  and  masses  included  in 
lime-breccia,  in  a  zone  parallel  with  the  bedding.  It  is  Arnold 
Hague's  opinion  that  the  Eberhardt  mine  probably  represents  the 
source  of  the  ore-solutions  which  impregnated  the  limestone,  wher- 
ever cavities  existed,  up  to  the  level  of  the  overlying  calcareous  slates, 
which  were  impermeable  to  the  solutions.  The  slate-cover  having 
been  removed  by  erosion,  the  ores  thus  accumulated  below  it  were  ex- 
posed immediately  at  the  surface;  and  the  surprisingly  large  pro- 
duct of  the  district  was  derived  from  open  cuts  and  shallow  work- 
ings. 

The  other  leading  analogue  in  Nevada  is  found  in  the  Eureka  dis- 
trict, and  was  made  widely  known  and  practically  significant  by  the 
law-suit  between  the  Eureka  and  Richmond  companies,*  which  in- 
volved the  definition  of  a  deposit  not  contemplated  in  the  United 
States  mining  law.  Similar  difficulties  have  arisen  under  the  old 
European  mining  codes.  Such  deposits  were  known  in.  some  dis- 
tricts of  Europe,  but  they  were  not  so  widely  distributed  as  the  fis- 
sure-veins, for  the  conditions  of  which  the  ancient  codes  were 
framed.  Conflicts  were  therefore  inevitable.  I  will  mention  only 
Bleiberg  in  Carinthia  (which  presents  some  degree  of  analogy  with 
Eureka)  where,  besides  the  general  mining  code,  special  statutes  be- 
came necessary,  departing  from  the  usual  rules  with  regard  to  pros- 
pecting and  the  location  and  the  acquisition  of  claims. 

*  R.  W.  Raymond,  "  The  Eureka-Richmond  Case,  "  Trans.  A.  I.  M.  E.,  1877, 
vi.,  371. 


THE   GENESIS   OF   ORE-DEPOSITS.  103 

The  geological  conditions  of  the  district  have  been  described  in  an 
elaborate  monograph  by  J.  S.  Curtis,*  based  on  the  developments 
existing  in  1882.  Further  knowledge  may  have  been  gained  since, 
but,  so  far  as  I  know,  nothing  later  has  been  published.  I  made  a 
brief  visit  iO  Eureka  in  1876  ;  but  as  no  comprehensive  maps  of  the 
mine-workings  were  then  available,  I  could  only  observe  in  a  general 
way  the  analogy  with  European  deposits  examined  by  me. 

According  to  Arnold  Hagne,f  the  series  here  occurring  of  Pros- 
pect Mt.  quartzite,  Prospect  Mt.  limestone,  Secret  Canon  shale,  and 
Hamburg  limestone,  is  Cambrian.  The  ore  is  confined  to  the  lime- 
stone first  named,  and  in  particular  to  a  portion  thereof  on  theN.  E.. 
slope  of  Ruby  Hill,  enclosed  between  two  fault-fissures.  The 
features  of  the  N*W. — SE.  ore-bearing  zone  are  too  variable  to 
be  indicated  by  a  normal  cross-section.  Fig.  76  shows  a  generalized 
and  Fig.  77  an  actual  section,  as  represented  by  Curtis. 

The  main  fault-fissure  separates,  in  the  upper  level,  the  massive 
limestone  in  its  hanging-  from  the  crushed,  ore  bearing  limestone  in 
its  foot-wall.  In  the  lower  levels  it  shows,  in  the  foot-wall,  quartzite 
with  intercalated  "  Lower  shale,"  and  in  the  hanging-wall,  further 
down,  shale  and  quartzite.  An  ideal  restoration,  above  the  present 
saddle  of  Ruby  Hill,  of  the  foot- wall  rocks  which  have  been  re- 
moved by  erosion,  would  bring  to  light  a  relative  displacement  of  150 
to  600  meters  (492  to  1968  feet),  the  indications  being  that  the  foot- 
wall  has  been  lifted.  This  would  explain  at  once  the  crushing  of  the 
limestone  in  the  foot-wall,  and  the  creation  of  a  second  fault  near 
the  contact  between  the  limestone  and  the  underlying  quartzite. 

The  ores  occur  chiefly  in  the  well-known  form  of  chimneys  and 
in  individual  masses,  mostly  interconnected  by  traces  of  ore,  at  least 
at  the  depth  where  the  two  faults  come  together.  In  the  mines  to 
the  SE.,  about  180  meters  (590  feet)  from  the  Eureka-Richmond 
boundary,  the  fissures  come  together  at  the  depth  of  about  400 
meters  (1312  feet),  the  line  of  their  intersection  thus  dipping  gently 
NW. 

The  ores  encountered  in  the  upper  zones,  above  water-level,  were, 
with  the  exception  of  a  few  insignificant  remains  of  sulphides 
(mostly  argentiferous  galena),  oxidized  ores,  such  as  cerussite  and 
anglesite,  chlorides,  etc.,  carrying  a  considerable  amount  of  silver  and 

*  "Silver-Lead  Deposits  of  Eureka,"  U.  S.  GeoL  Surv.,  Monogr.  vii.,  Wash- 
ington, 1884. 

f  "  Abstract  of  Report  on  the  Geology  of  the  Eureka  District,"  Third  Ann.  Rep. 
of  U.  S.  GeoL  Surv.,  1881-1882,  Washington,  1883,  p.  241. 


104  THE   GENESIS   OF   ORE-DEPOSITS. 

a  little  gold.  The  present  water-level  follows  approximately  the 
line  of  intersection  of  the  two  faults,  but  the  fact  that  oxidized  ores 
have  been  found  still  deeper  indicates  that  the  water-level  was  once 
lower  down. 

It  might  consequently  be  expected  that  caves  formed  fcy  the  vadose 
circulation  would  also  occur  at  considerable  depths,  especially  as  the 
whole  wedge  of  limestone  is  traversed  by  ore-shoots,  the  oxidation 
of  which  would,  of  course,  give  occasion  for  cave-formations.  The 
newly-formed  caverns  would  often  lie  along  the  ore-channels,  and 
especially  in  their 'upper  portions.  (See  J.  S.  Curtis,  1.  c.,  p.  100.) 

Some  of  the  irregularly  distributed  ore-bodies  follow  rather  the 
quartzite-limestone  contact ;  others  rather  the  main  fissures,  with  a 
NW.  dip,  like  that  of  the  limestone  wedge.  Of  the  two  largest 
bodies,  which  have  furnished  the  chief  product  of  the  district,  the 
east  ore-body  exhibits  a  steep  SE.  pitch  for  nearly  400  meters  (1312 
feet),  and  the  west  ore-body,  for  nearly  an  equal  distance,  a  flat 
NW.  pitch. 

In  considering  their  structure,  we  must  distinguish  sharply  between 
their  original  and  their  decomposed  condition.  The  latter  often 
hinders  a  clear  recognition  of  the  former.  The  strata-like  deposits 
of  cerussite  and  other  products  of  decomposition  mentioned  by  Cur- 
tis (L  c.,  p.  98)  are  perhaps,  like  those  in  my  sketch,  Fig.  78,  from 
the  Old  Telegraph  mine,  remains  of  the  original  crusti  Scat  ion,  and 
his  statement  (p.  104)  that  "  when  the  ore  is  not  oxidized  there  are 
no  signs  of  a  banded  or  concentric  structure,  and  the  phenomena  ob- 
served point  entirely  to  substitution  of  the  sulphurets  for  country- 
rock,"  may  thus  be  explained.  In  like  manner  his  assertion,  in  the 
same  place,  that  "  the  internal  structure  of  the  ore-masses  in  no  way 
resembles  those  of  Raibl,"  is  so  far  correct  that  the  original  filling  is 
at  Raibl  extraordinarily  distinct,  and  at  Eureka,  on  the  contrary,  per- 
haps, only  obscurely  traceable. 

I  personally  saw  in  the  Eureka  mine  some  small  ore-masses,  which 
exhibited  crustification,  if  not  in  a  striking  degree,  yet  sufficiently  to 
be  recognized  by  an  impartial  observer.  Mr.  Curtis  himself  (I.  c.,  p. 
98)  says  that  "rounded  boulders  of  limestone  as  a  nucleus"  occa- 
sionally occur  in  the  ore-mass,  and  that  in  a  limestone-breccia  "  small 
masses  of  ore  sometimes  completely  fill  the  spaces  between  the 
limestone  walls," — two  phenomena  which  indicate  crustification, 
and  are  explained  by  the  hypothesis  of  a  filling  of  pre-existent 
spaces. 

A  metasomatic  removal  of  the  limestone,  such  as  has  taken  place 


THE    GENESIS   OF   ORE-DEPOSITS.  105 

in  the  secondary  calamine-cleposits  of  Raibl,  cannot  well  be  supposed 
for  the  original  ore-deposition  at  Eureka,  but  may  have  attended  the 
formation  of  the  secondary,  decomposed  products. 

I  believe  that  later  mining  in  deeper  zones  has  developed  more 
clearly  the  structure  of  the  original  Eureka  deposits,  and  that  speci- 
mens of  the  ore  have  shown,  after  polishing,  traces,  at  least,  of  crus- 
tification. 

In  short,  I  consider  the  original  Eureka  ores  to  have  been  deposi- 
ted in  pre-existing  spaces  by  ascending  mineral  solutions,  while  their 
decomposition  and  the  formation  of  the  caverns  are  the  effects  of 
descending  surface-waters. 

I  agree  with  Mr.  Curtis  that  the  ore-solutions  ascended  from  the 
deep  region  through  the  "  main  fissure  "(which  has,  in  the  NW.  the 
character  of  a  Blatt  at  Raibl,  and  in  the  SE.  part  of  the  district  is 
filled  with  rhyolite),  and  that  they  formed  and  filled  the  ore-channels 
in  the  soluble,  fissured  limestone. 

Missouri  and  Wisconsin. — We  have  dealt  thus  far  with  ore-deposits 
in  mountain  districts,  where  tilting  and  folding,  as  well  as  the  occur- 
rence of  eruptives,  betray  a  disturbance  of  the  original  relations  of 
stratification.  But  there  are  also  deposits  in  limestone  in  plateau- 
regions,  where  the  strata  show  no  considerable  disturbance.  Under 
this  head  two  great  districts  deserve  attention  ;  namely,  the  lead- 
regions  of  Missouri  and  Wisconsin. 

Concerning  the  former,  we  may  refer  to  a  number  of  more  or  less 
detailed  descriptions.* 

We  have  in  this  case  not  a  perfect  plateau,  since  here  and  there 
domes  of  the  underlying  ArchaBan  come  to  the  surface,  as  especially 
in  the  continuation  of  the  Ozark  mountains;  but  the  predominant 
character  is  nevertheless  that  of  a  structural  plateau.  The  ore-de- 
posits, chiefly  confined  to  the  Silurian  limestone,  are  in  part  primary 
xenogenous  and  in  part  hysteromorphous  (debris)  deposits ;  the  lat- 
ter, as  is  well  known,  consist  of  the  detritus  from  the  weathering 
and  erosion  of  the  outcrops  of  the  former.  In  the  former,  we  find 
all  the  phenomena  encountered  in  the  deposits  of  mountain  regions. 
One  of  these  is  peculiarly  developed,  namely,  the  gently  inclined 

*  J.  R.  Gage,  "  Lead-Mines  of  S.  E.  Missouri,"  Geol.  Snr.  of  Mo.,  1873-4,  p. 
603,  and  Trans.  A.  I.  M.  E.,  Hi.,  116. 

G.  C.  Broadhead,  "The  S.  E.  Mo.  Lead-Districts,"  Ibid.,  p.  100. 

A.  Schmidt  and  A.  Leonhard,"  The  Lead- and  Zinc-Region  of  S.  W.  Mo,"  Geol. 
Surv.  of  Mi.,  1873-4,  p.  384. 

A.  Schmidt,  "The  Lead-Region  of  Central  Missouri,"  Ibid.,  p.  503. 


103  THE   GENESIS   OF   ORE-DEPOSITS. 

cavities  or  ore-channels,  shown  in  the  Valle  and  Bish  mines  of  Jef- 
ferson and  St.  Francis  counties,  concerning  which  J.  R.  Gage  has 
given  some  (unfortunately  not  very  clear)  notes  and  sketches. 

In  the  Valle  mines,  a  shaft  49.9  meters  (164  feet)  deep,  situated 
33.5  meters  (110  feet)  above  the  valley-bottom,  encountered  at  three 
different  depths,  respectively  of  44.5,  46.3,  and  49.9  meters  (146, 
151  and  164  feet)  flat-lying  ore-channnels,  1  to  2  meters,  (3  to  6 
feet)  wide,  which,  winding  in  different  directions,  produce  networks, 
connected  at  the  intersecting  points  by  chimneys  from  one  level  to  the 
other.  The  cross-section  of  these  channels  in  the  horizontal  lime- 
stone or  dolomite  contracts  sometimes  to  a  few  square  centimeters, 
or  enlarges  to  several  square  meters,  with  a  height  of  3  to  4  meters 
(10  to  12  feet). 

The  original  metallic  filling  was  galena,  pyrite  and  zincblende, 
but  is  already  oxidized  to  cerussite,  anglesite,  smithsonite  and  cala- 
rnine,  which  are  accompanied  with  barite  and  a  red  clay.  We  are 
specially  interested  in  the  original  structure  of  this  filling  ;  but  this 
is  not  easily  detected  in  the  mere  diagrams  at  hand. 

Figs.  32  to  35  reproduce  four  of  Mr.  Gage's  sections,  the  first 
three  being  Figs.  17,  18  and  19  of  his  paper  in  these  Transactions, 
and  the  fourth,  Fig.  72  of  his  article  in  the  report  of  the  Missouri 
survey.  They  indicate  for  both  the  metamorphosed  and  the  original 
mineral  crusts  a  prevailing  horizontal  position,  so  that  we  might 
conclude  that  the  deposits  took  place  in  cavities,  the  upper  portions 
of  which  were  filled  with  gas  only.  A  very  peculiar  formation  is 
the  red  clay  which  in  some  instances  covers  the  walls  of  the  caverns 
and  surrounds  on  all  sides  the  central  filling.  The  data  at  hand 
afford  no  clue  to  its  origin. 

Mr.  Gage's  description  of  Fig.  35  (/.  c.,  p.  618)  is  as  follows  : 

"Fig.  [72]  represents  the  occurrence  of  these  minerals.  The  solid  limestone 
contains  a  fissure,  entirely  filled  with  minerals  and  gangue.  The  minerals  are 
completely  enveloped  by  the  red  clay.  Above  are  two  thin  folds  of  silicate  of 
zinc,  separated  from  each  other  and  from  the  limestone  by  the  red  clay.  The  folds 
of  the  zinc-ore  are  sometimes  perfectly  solid,  being  from  one  to  six  inches  thick, 
and  consisting  of  alternate  layers  of  the  same  material  in  very  compact  folds; 
again,  the  mass  of  zinc-ore  is  from  one  to  six  inches  in  thickness,  but,  instead  of 
being  dense,  consists  of  a  thin  crust,  with  a  cavity,  whose  interior  walls  are  lined 
with  beautiful,  brilliant  crystals  of  the  silicate  and  occasionally  the  carbonate  of 
zinc.  More  rarely,  crystals  of  galena  are  in  the  cavities,  but,  in  this  case,  are 
invariably  covered  with  a  thin  coating  of  the  silicate;  and  not  infrequently  portions 
of  the  cavities  are  partially  filled  with  red  clay,  highly  impregnated  with  oxide  of 
iron,  and  having  the  appearance  of  a  highly-decomposed  brown  hematite.  Occa- 
sionally, heavy  spar  (barytes)  lies  in  a  dense  mass  in  close  contact  with  the  zinc- 


THE   GENESIS   OF   ORE-DEPOSITS.  107 

ore;  but  more  frequently  it  is  associated  with  the  galena.  Often,  but  not  invaria- 
bly, immediately  below  the  folds  of  zinc-ore,  occur  irregular  masses  of  the  zinc-ore 
in  the  crystallized  form,  as  pseudomorphs  of  galena,"  etc. 

All  the  doubts  which  arise  concerning  the  mode  of  this  formation 
would  probably  be  solved  by  a  series  of  objective  pictures  of  it ;  and 
it  is  to  be  hoped  that  an  occurrence  so  interesting  theoretically  will 
be  accurately  recorded  before  it  is  too  late. 

The  deposits  occurring  near  the  "  islands  "  of  granite  and  por- 
phyry, have  special  interest.  While  the  Silurian  limestones  of  the 
surrounding  country,  farther  from  these  islands,  present  chiefly  only 
lead-  and  zinc-ores,  other  metals,  such  as  copper,  cobalt,  and  nickel, 
occur  as  the  Archaean  foundation-rocks  are  approached ;  and  this 
circumstance  is,  to  my  mind,  an  indication  that  the  source  of  the 
lead-deposits  also  is  to  be  sought  in  depth. 

Mine  la  Motte. — As  an  example,  I  may  cite  the  district  of  Mine 
la  Motte,  to  which  I  once  made  a  brief  visit*  The  rock  here  is 
usually  the  same,  namely,  a  Cambrian  dolomite,  containing,  how- 
ever, sandy  portions  and  a  clayey  stratum  characterized  by  numerous 
fossils  (Linguld).  The  ore  occurs  predominantly  as  an  impregnation 
in  the  rock,  more  concentrated  in  a  given  zone.  The  so-called  sand- 
stone does  not  here,  as  in  other  instances,  cut  off  the  impregnation  ; 
it  is,  in  fact,  only  a  sandy  limestone  and  dolomite,  and  its  carbonates 
can  be  replaced  by  ore  as  well  as  those  of  adjoining  strata. 

I  thought  that  I  noticed  in  the  open  workings  called  the  Jack  and 
the  Seed-tick  diggings  a  very  remarkable  phenomenon  ;  namely,  the 
ore-impregnation  in  the  almost  horizontal  stratified  rock  was  con- 
formable not  to  the  bedding  but  to  planes  crossing  it  at  a  very  acute 
angle  (about  10°).  A  pretty  long  terrace  was  exposed  ;  and  the  im- 
pregnation-planes cut  pretty  regularly  through  the  sandy  dolomite 
also.  This  appearance  indicates  plainly  a  later  formation  of  the  ore, 
independent  of  the  deposition  of  the  rock-strata  ;  and  one  is  almost 
involuntarily  forced  to  believe  that  it  was  the  former  ground-water 
surface  which  formed  the  cavities  to  be  impregnated.  But  it  was, 
and  is,  inconceivable  to  me  how  these  cavities  could  be  filled  with 
sulphides;  and  I  can  only  urge  that  occurrences  of  this  kind  should 
be  subjected  to  a  more  thorough  study  than  it  has  been  in  my  power 
to  give  to  them. 

Wisconsin. — In  Wisconsin,  and  in  parts  of  Iowa  and  Illinois,  there 
is  an  extensive  true  plateau,  the  calcareous  members  of  which  con- 
tain many  and  various  deposits  of  lead-  and  zinc-ores.  An  excel- 
lent monograph  concerning  them,  by  my  esteemed  friend,  Prof.  J. 


108  THE   GENESIS   OF   ORE-DEPOSITS. 

D.  Whitney,*  is  at  hand.  The  author  seeks  to  show  that  the  min- 
eral solutions  depositing  these  ores  came  from  above,  not  from  below. 
He  appeals  to  the  circumstance  that  of  the  two  stratified  formations, 
the  upper  and  the  lower  Magnesian  limestone  (underlain  by  an  upper 
and  a  lower  sandstone,  respectively),  the  ores  occur  chiefly  in  the 
upper,  and  only  seldom,  and  in  small  quantity,  in  the  lower;  while 
the  two  sandstones  (the  lower  of  which  is  assigned  to  the  Potsdam) 
do  not  reveal  any  traces  of  ore,  as  they  should  do  if  the  solutions  had 
come  from  below.  I  confess  that  this  conclusion  is  not  obvious  to 
me.  There  may  have  been  a  passage  through  these  sandstones  at  a 
distant  point,  not  yet  exposed  ;  and  the  mineral  solutions  may  have 
found  or  created  spaces  in  the  soluble  rock. 

The  argument  that  the  ores  must  have  come  from  above  because 
it  has  not  been  possible  to  discover,  in  the  Wisconsin  region,  fault- 
fissures  and  eruptive  dikes,  such  as  have  brought  up  similar  ores  in 
the  north  of  England  and  other  places,  seems  to  me  likewise  incon- 
clusive. And  as  little  can  I  accept  the  explanation  of  an  occurrence 
near  Dubuque,  discovered  by  T.  Lavins  and  described  by  Whitney 
(op.  cit.y  p.  291  and  Fig.  on  p.  392),  which  I  reproduce  in  Fig.  79. 
The  fragments  of  galena,  crusted  with  cerussite,  which  hang  from 
the  roof  of  a  natural  cavern,  are  taken  as  a  proof  that  the  solutions 
which  deposited  them  must  have  come  from  above.  But  a  continu- 
ation of  this  cavern  is  indicated  in  the  bottom,  filled  with  clay, 
mixed  with  scattered  pieces  of  galena.  In  my  opinion,  this  was 
doubtless  originally  the  filling  of  a  vertical  fissure,  which  was  en- 
larged by  the  ground-water,  as  indicated  by  the  dotted  line.  The 
symmetrical  crusts,  as  I  suppose,  of  that  filling  were  in  part  broken 
up,  and  fell  into  the  clay  accumulating  in  the  space  below;  while 
the  upper  part  of  the  filling  remained  attached  to  the  rock  of  the 
roof. 

3.  MET  AMORPHOUS  DEPOSITS. 

Metamorphism  has  been  most  truly  defined  by  A.  de  Lapparent 
as  the  sum  of  the  chemical  changes  undergone  by  the  sedimentary 
rocks  after  their  deposition.  General  or  regional  metamorphism, 
affecting  the  rocks  over  wide  areas,  is  distinguished  from  local  or 
contact-metamorphism,  caused  in  certain  groups  of  strata  by  eruptive 
intrusions.  In  studying  the  occurrence  of  useful  minerals,  we  oc- 
cupy rather  the  local  standpoint,  and  start  with  an  assumed  original 

*  Report  of  a  Geological  Survey  of  the  Upper  Mississippi  Lead-Region,  Albany, 
1862. 


THE   GENESIS   OF   ORE-DEPOSiTS.  109 

condition  of  the  rock,  though  its  really  original  character  may  not 
always  be  demonstrable— understanding  thereby,  for  our  purpose,  a 
so-called  typical  condition,  usually  shown  at  most  places  where  the 
rock  occurs. 

We  distinguish  the  replacement  of  some  constituents  of  a  com- 
pound rock,  for  which  the  term  "  impregnation  "  is  more  appropri- 
ate, from  the  replacement  of  the  whole  homogeneous  mass  by  meta- 
somasis.  But  since  every  rock  undoubtedly  contains  small  primitive 
cavities,  it  is  difficult,  and  sometimes  impossible,  to  decide  whether 
a  new,xenogenous  substance  has  not  been  deposited  in  such  pores;  and 
a  case  of  this  kind  would  fall  under  our  notion  of  impregnation.  The 
new  substance  may  indeed  have  found  entrance  through  the  pores, 
if  the  mineral  solutions  were  under  sufficient  pressure  to  overcome 
the  friction  of  their  walls,  at  least  in  the  line  of  least  resistance ; 
and  these  solutions,  thus  introduced,  may  attack  and  replace  one  or 
another  element  of  the  rock.  The  entrance  of  such  solutions  will  be 
greatly  facilitated  by  the  fissuring  of  the  rock,  whether  by  internal 
or  external  forces.  We  find  in  connection  with  ore  veins,  and  also 
with  the  thinnest  mere  seams,  an  impregnation  of  the  country-rock, 
which  Cotta  has  called  subordinate  or  dependent  (unselbstdndige) 
impregnation. 

The  particles  of  certain  substances  possess  a  peculiar  mutual  at- 
traction. In  the  sandstone  of  Fontainebleau  occur  aggregates  of  cal- 
oite  crystals,  which  have  come  together  in  spite  of  the  separating 
medium  of  sandstone  ;  and  in  a  similar  way,  as  we  have  seen,  another 
substance  of  strong  crystallizing  power,  namely,  galenite,  forms,  in 
the  pipe-ores  and  script-ores  of  Raibl,  crystalline  masses,  in  spite  of 
the  intervening  diaphragm  of  a  foreign  medium. 

In  like  manner  are  formed  the  so-called  concretions,  the  calcare- 
ous and  marly  masses  (Losskindlein)  in  the  Loess,  and  the  Marleker 
of  the  ancient  Scandinavian  beaches.  For  the  formation  of  the 
former,  occasion  was  given  by  decaying  plant-roots  ;  for  that  of  the 
latter,  by  various  animal  remains,  mussels,  fishes,  etc.  In  Norway, 
they  have  preserved  a  complete  fauna  of  the  Glacial  and  post- 
Glacial  epochs. 

Similarly,  we  find  in  some  spherosiderite  concretions  of  the  Saar- 
briicken  coal-basin  the  remains  of  fishes.  A  discernible  nucleus  is 
not  always  found  in  such  concretions;  sometimes  no  cause  for  this 
peculiar  formation  can  be  discovered.  The  concretions  occurring  in 
stratified  rocks  are  usually  lenticular,  comprising  portions  of  several 
similar  strata.  Even  spherical  forms,  resembling  pisolites,  occur. 


110  THE   GENESIS   OF   ORE-DEPOSITS. 

If  we  imagine,  for  instance,  spherosiderite  concretions  formed 
closely  side  by  side  in  one  stratum,  we  shall  have  a  regular  bed  of 
clay-ironstone.  Leaving  out  of  view  the  agency  of  fissures,  or  con- 
tacts with  intruded  rocks,  impregnations  following  certain  strata 
may  be  formed,  constituting  a  second  kind  of  ore-beds.  A  third 
kind  may  result  from  the  more  or  less  complete  replacement  of  the 
original  rock,  especially  when  the  latter  is  a  soluble  precipitate,  like 
gypsum  or  limestone.  In  thick  limestone  formations  the  ore-beds 
occur  at  the  contact  with  insoluble  rocks,  as  at  Rodna. 

In  all  these  cases  the  deposits  have  the  form  of  a  bed,  but  the 
ores  rarely  cover  the  whole  contact-surface,  occupying,  on  the  con- 
trary, only  certain  zones  of  it.  In  other  words,  in  these  as  in  other 
deposits,  ore-shoots  occur. 

Much  more  complicated  relations  result  when  the  mineral  solu- 
tions ascend  along  structural  fissures  and  rock-contacts  ;  and  in 
order  to  a  comprehensive  description  of  this  suite  of  phenomena,  it 
will  be  well  to  consider  first  the  simpler  conditions  obtaining  in 
soluble  rocks,  and  afterwards  the  more  complex  occurrence  of  such 
deposits  in  crystalline  and  eruptive  rocks.  We  will,  therefore,  re- 
view the  metamorphous  deposits  as  they  occur  in  (a)  distinctly  strati- 
fied rocks;  (b)  soluble  precipitates;  and  (c)  crystalline  schists  and 
eruptive  rocks. 

a.  Metamorphous  Ore-Deposits  in  Distinctly  Stratified  Hocks. 

We  find  in  unquestionable  sediments  not  only  metallic  oxides  and 
salts,  but  also  sulphides,  in  the  form  of  ore-beds  which,  by  reason 
of  this  stratigraphical  relation,  have  been  held  to  be  of  contempora- 
neous origin,  that  is,  idiogenous.  As  a  consequence,  it  has  been 
necessary  to  assume  that  they  were  precipitated  in  a  sea-basin,  in 
which,  before  and  after  their  precipitation,  only  barren  sediments 
were  deposited.  These  metals  must,  therefore,  have  been  dissolved 
in  the  water  of  the  basin,  and  that  in  very  large  quantity,  as  indi- 
cated by  the  frequently  great  thickness  of  the  ore-beds.  But  for 
such  an  assumption  we  have  no  present  analogy. 

The  Deposition  o/  Ores  from  Sea-Water. — In  this  particular, 
however,  we  have  to  do  rather  with  suggestions  than  with  demon- 
strations of  fact.  So  far  as  sea- water  is  concerned,  traces  of  metals 
have  been  found  in  the  water  itself,  in  the  ashes  of  marine  plants, 
and  in  the  solid  constituents  of  marine  animals,  for  instance,  corals, 
by  Malagutti,  Bibra,  and  Forchhammer.*  Traces  of  silver,  iron, 

*  G.  Bischof,  Ckem.u.  Phys.  Geologic,  vol.  i.,  Bonn,  1843,  pp.  445-447. 


THE   GENESIS   OF   ORE-DEPOSITS.  Ill 

and  manganese  were  detected  in  the  water,  and  lead,  zinc,  cobalt, 
and  nickel  in  the  marine  organisms ;  and  since  there  are  in  sea- 
water  small  amounts  of  hydrogen  sulphide,  Bischof  considers  the 
deposition  of  metallic  sulphides  from  the  sea  to  have  been  possible. 
He  observes  (op.  cit.,  p.  432)  that  the  occurrence  of  metallic  sulphides 
in  sedimentary  rocks,  such  as  that  of  copper  and  silver  sulphides  in 
Kupfcrschiefer,  or  that  of  lead  sulphide  in  Buntsandstein,  may  be 
thus  explained ;  and  even  indulges  (p.  836)  in  the  following  teleo- 
logical  conclusion  : 

"Since  it  cannot  be  doubted  that  the  rivers  flowing  into  the  ocean  bring  with 
them  metallic  salts,  though  in  very  dilute  solution,  it  seems  a  wise  arrangement  that 
in  the  hydrogen  sulphide  of  sea-water  a  precipitant  is  presented  to  throw  down  the 
smallest  minima,  and  thus  to  prevent  the  gradual  accumulation  of  substances  so  in- 
jurious to  animal  life" 

Of  the  various  metals  dissolved  in  sea-water,  iron  is  least  injurious 
to  animal  life.  Indeed,  animal  life  assists,  in  the  so-called  lake- 
ores,  the  segregation  of  this  metal.  Moreover,  the  precipitation  of 
ferrous  and  ferric  oxides  from  concentrated  solutions  is  probable,  so 
that  a  precipitation  of  iron-ores  directly  from  sea-water  seems  to  be 
established  as  a  possible  origin  for  some  iron-ore  beds. 

But  the  conveyance  of  metallic  salts  by  rivers  to  the  ocean  and  the 
formation  of  hydrogen  sulphide  in  sea- water  are  unquestionably  con- 
tinuous; and  the  precipitation  of  metallic  sulphides  must,  therefore, 
have  taken  place  uniformly  in  all  sediments  and  precipitates  of  the 
ocean  ;  whereas,  we  find  the  ore-beds  in  fact  only  in  certain  strata.  If 
these  are  to  be  thus  explained,  we  must  assume  that  the  ocean  was  at 
certain  periods  much  more  strongly  impregnated  with  metallic  salts 
— a  scarcely  tenable  hypothesis  as  applied  to  the  mighty  deep, — or  we 
must  suppose  with  Carnal  1,  as  H.  Hoefer  has  recently  done,*  a  sub- 
sequent re-deposition  of  the  primitive  metallic  salts,  contained  in 
minute  quantities  in  the  sea-deposits — in  other  words,  their  solution 
and  re-precipitation  at  certain  horizons.  Hoefer  cites  the  l£ad-  and 
zinc-deposits  of  Upper  Silesia  and  other  districts,  which  occur  in 
marine  Triassic  limestones.  He  assumes  the  maintenance  of  uniform 
horizons  by  these  deposits  to  be  demonstrated,  but  points  out  that 
some  of  these  horizons  were  already  ore- bearing  when  first  formed. 

In  short,  a  number  of  investigators  have  adopted  the  hypothesis 
of  an  original  ore-deposition  from  the  ocean,  without  giving  any 

*  "  Die  Entstehung  der  Blei-,  Zink-  u.  Eisenlagerst.  in  Oberschlesien." — Oesterr 
Zeitsch.f.  Berg.  u.  H-wesen,  1893,  xli.,  p.  82. 


112  THE   GENESIS   OF   ORE-DEPOSITS. 

other  reason  than  the  observed  relations  of  stratification.  Yet,  in  a 
considerable  experience  with  ore-deposits  in  marine  limestones,  I  have 
never  been  able  to  find  genuine  ore-beds  among  them,  but  always  only 
ores  of  subsequent  introduction;  so  that  I  feel  warranted  in  believ- 
ing that  such  ore- beds  proper  do  not  exist. 

As  to  the  primitive  ore  contained  in  marine  sediments  and  pre- 
cipitates, innumerable  chemical  analyses,  especially  of  limestone, 
have  failed  to  show  the  metallic  traces  which,  according  to  the  above 
hypothesis,  should  be  present.  For  this  reason,  as  I  have  already 
observed,  even  Sandberger  did  not  venture  to  derive  the  metals 
from  the  limestone,  preferring,  for  instance,  at  Raibl,  to  look  to  the 
overlying  slates. 

The  maintenance  of  certain  ore-bearing  horizons  was  set  up  by  A. 
von  Groddeck,  to  render  more  plausible  the  notion  of  a  direct  depo- 
sition from  the  ocean  ;  but  I  do  not  believe  it  possible  to  prove  such 
an  identity  of  horizon  for  different  ore-deposits.  Similar  ores  and 
stratigraphical  conditions  are  not  confined  to  the  Trias.  On  the 
Rhine,  in  England  and  in  America  they  occur  at  much  lower  hori- 
zons in  the  Paleozoic  rocks.  Even  in  Carinthia  the  ore-bearing 
limestones  of  the  richest  deposits  do  not  occupy  the  same  horizon. 
That  of  the  Raibl  slate  is  very  different  from  that  of  the  Bleiberg 
slate  (carrying  Ammonites  aori),  and  the  deposits  in  these  localities 
are  by  no  means  beds,  but,  as  I  have  shown,  channels  in  the  lime- 
stone, filled  with  ore. 

Ore- Deposition  in  Fresh  Water. — The  demonstration  of  direct  ore- 
deposition  in  fresh-water  strata  encounters  the  same  difficulties, 
though  it  may  be  supported  by  the  same  chemical  speculations. 
Here  the  hypothesis  is  favored  by  the  analogy  of  the  lakes  of  regions 
without  drainage  to  the  sea,  in  which  the  salts  brought  in  by  rivers 
are  necessarily  concentrated  by  evaporation.  But  since  organic  life 
is  restricted  in  these  salt  lakes  to  a  few  animal  species,  the  analogy 
can  hav%  but  a  limited  application.  Moreover,  it  would  be  neces- 
sary to  suppose  cataclysmic  changes,  like  the  interposition  of  a 
period  of  no  drainage  in  the  midst  of  an  epoch  of  fresh-water  sedi- 
mentation. 

Without  the  assumption  of  such  cataclysms,  I  do  not  believe  that 
the  Mannsfeld  Kupferschiefer,  in  which  the  organic  (fish)  remains 
can  be  traced  continuously  from  foot-  to  hanging-wall,  could  be  ex- 
plained in  this  way.  It  deserves  mention,  that  some  of  the  earlier 
geologists,  like  Freiesleben,  accepted  the  sometimes  contorted  attitudes 
of  the  Palceoniscus  in  the  Kupferschlefer  as  a  proof  of  contempora- 


THE   GENESIS   OF   ORE-DEPOSITS.  113 

neous  ore-depositions,  and  alleged  that  these  fishes  had  been  thrown 
into  violent  contortions  by  the  copper-solution,  in  which  condition 
they  died  and  were  buried  in  the  sediment.  The  naivete  of  this 
diagnosis  (which,  nevertheless,  some  modern  writers  have  not  hesi- 
tated to  repeat),  is  evident.  Contorted  fish-remains  occur  in  other 
formations  outside  of  the  Kupfersehiefer,  and  clearly  show  the  ad- 
vanced state  of  decomposition  in  which  the  bodies  reached  the  sedi- 
ments. 

The  Kupferschiefer  of  Mannsfetd. — The  Mannsfeld  Kupferschiefer, 
as  is  well  known,  is  a  thin  bed  of  bituminous  slate,  lying  between 
the  Permian  sandstone  below,  and  the  marine  member  of  the  same 
formation,  the  Zechstein,  above,  and  containing  sulphides  of  copper, 
silver,  lead,  zinc,  antimony,  mercury,  nickel  and  cobalt.  The  copper 
amounts  to  20  to  30  kilograms  (44  to  66  pounds),  and  the  silver 
to  125  to  150  grammes  (4  to  5  ounces,  Troy),  per  metric  ton  of  2204 
pounds.  In  polished  sections,  the  ore  can  be  seen  in  thin  leaves  lying 
between  lamina  of  slate,  and  often  accompanied  by  gypsum.  But 
the  same  ores  occur  in  scattered  bunches  in  the  sandstone  below, 
and  small  bodies  of  redruthite  are  found  in  the  limestone  above.* 
This  circumstance  alone,  that  ore  occurs  also  in  the  marine  lime- 
stone, above  the  fresh-water  Kupferschiefer,  is  unfavorable  to  the 
contemporaneous  origin  of  ore  and  rock. 

Kupferschiefer  in  Thuringia  and  Bohemia. — The  same  bituminous 
slate  occurs  in  the  Thuringian  forest  on  the  south  slope  of  the  Hartz, 
and  in  other  points  a  considerable  distance  away.  It  must  therefore 
have  been  deposited  in  a  large  basin.  But  it  is  a  question,  whether 
it  anywhere  carries  ore  and  deserves  the  name  of  Kupferschiefer. 

In  NE.  Bohemia,  the  same  Permian  slate,  with  almost  the  same 
fossils,  is  widely  distributed,  but  without  the  marine  member  which 
covers  it  in  Germany.  The  Permian  of  Bohemia  carries  copper-ores 
in  many  places;  and  in  one  locality,  namely,  at  Hermannseifen, 
these  ores  occur  in  the  bituminous  slate,  which  might  properly  here 
be  called  Kupferschiefer.  I  had  opportunity  in  1858  to  examine  the 
mines.  The  richness  in  metal  was  not  unsatisfactory  ;  but  there  was 
much  complaint  of  the  numerous  faults  which  seriously  enhanced  the 
difficulty  of  mining. 

Precisely  the  same  difficulty  exists  at  Mannsfeld  and  in  the  Thur- 
ingian forest,  as  Cotta  (op.  cit ,  §  50),  reports  in  part  as  follows : 

"  The  fault-fissures  themselves,  are,  however,  rarely  ore-bearing,  yet  often  seem 

*  See  Grocldeck's  Erzlagerstatten,  \  58,  and  Cotta's  manual,  g  50. 

8 


114  THE   GENESIS   OF   ORE-DEPOSITS. 

nevertheless  to  have  influenced  the  ore-bearing  character  of  the  strata  traversed  by 
them.  This  influence  is  shown  in  the  increase  or  diminution  of  the  proportions  of 
ore,  not  only  in  the  immediate  neighborhood,  but  sometimes  also  for  a  considerable 
distance,  even  as  far  as  the  next  master-fault.  It  is  shown  also  in  the  transfer  of  the 
metallic  contents  from  one  stratum  to  another." 

This  and  other  observations  concerning  the  influence  of  the  faults 
upon  the  ore-distribution  bear  decidedly  against  the  contemporaneity 
of  the  ore-deposits,  and  in  favor  of  a  later  introduction  of  ore 
through  the  fault-fissures. 

But  this  conclusion  becomes  much  clearer  upon  a  consideration  of 
the  remaining  occurrences.  Thus,  according  to  Cotta  (op.  ciLj  §  39), 
the  Kupferschiefer  at  the  edge  of  the  Thuringian  forest  is  not  so  rich 
in  ore  as  on  the  southern  border  of  the  Hartz.  More  important  than 
the  copper-slate  itself  are  the  fault-fissures  which  traverse  the  whole 
group  of  strata,  but  only  carry  ore  in  certain  zones  in  which  they  in- 
tersect certain  strata — the  Kupferschiefer  among  them.  "Strange  to 
say,"  observes  Cotta,  "  near  Camsdorf  it  is  almost  exclusively  where 
the  Kupferschiefer  has  suffered  such  disturbances  that  it  is  rich 
enough  to  repay  mining."  In  speaking  of  Riegelsdorf  he  says, 
"The  cobalt-ores  have  in  some  cases  made  their  way  from  the  veins 
into  the  country-rock." 

Westphalia. — At  Stadtberg  (op.  cit.,  p.  76),  in  Westphalia,  there  are 
even  several  copper-bearing  strata,  and  these  are  cut  by  copper-bear- 
ing veins.  At  Bieber,  veins  traverse  the  whole  group  of  strata  into 
the  underlying  mica-slate,  and  "  the  irregularly  distributed  ore 
occurs,  strange  to  say,  chiefly  interleaved  in  the  mica-slate,  and  not, 
as  in  the  Hartz  and  the  Thuringian  forest,  in  the  horizon  of  the 
Kupferschiefer;  while,  on  the  other  hand,  the  impregnations  from 
the  veins  have  penetrated  chiefly  the  bituminous  marly  slate." 

In  consideration  of  the  expressions  partly  quoted  verbatim  above, 
it  is  difficult  to  see  how  there  can  be  any  doubt  of  the  secondary 
nature  of  the  ore-deposits  in  the  Kupferschiefer  throughout.  Yet 
Groddeck*  has  reproved  me  for  coming  to  this  conclusion.  He  says 
himselff  expressly  (evidently  having  in  mind  the  typical  Mannsfeld 
occurrence) : 

"The  ores  were  laid  down  contemporaneously  with  the  slime-deposit,  the  bitumi- 
nous marly  slate  as  the  ore-matrix."  .  .  .  .  "It  is  entirely  impossible  that  the  ores 
could  have  entered  the  bed  somehow  from  the  fissures,  at  a  later  period,  after  the 
covering  of  the  marly  slate  with  more  recent  rocks.  If  we  assume  that  the  ore- 

*  "  Bemerk.  zur  Classification  d.  Lagerstatten,"  B.  u.  H.  Zlg.,  1885. 
f  Erzlagerstallenlehre,  g  142. 


THE   GENESIS   OF   ORE-DEPOSITS.  115 

solutions  were  introduced  through  the  fissure  faulting  the  bed,  it  remains  inconceiv- 
able why  the  filling  of  metallic  sulphides,  through  a  field  of  many  square  miles, 
should  be  uniformly  and  exclusively  confined  to  the  stratum  of  marly  slate,  about  £ 
meter  (19.5  inches)  thick,  and  should  not  also  occur  more  or  less  near  the  fissures 
in  the  strata  above  and  below,  there  being  in  these  no  lack  of  carbonates  and  bitu- 
minous constituents,  available  as  precipitants  of  the  solutions — the  Stinkschiefer, 
for  instance,  Iving  not  far  above  the  Kvpferschiefer,  being  rich  in  such  sub- 
stances." 

Groddeck  here  overlooked  the  principle,  elsewhere  urged  by  him, 
that  a  single  link  in  a  whole  chain  of  phenomena  should  not  be  ex- 
clusively considered.  He  contemplated  only  the  special  develop- 
ment at  Mannsfeld ;  assumed,  moreover,  similar  developments  for 
many  square  miles,  which  show  in  fact  many  variations,  and  did  not 
take  into  account  the  circumstance  that  when  the  Kupferschiefer  is 
not  cut  bv  fault-fissures,  it  is  also  not  valuable  for  mining.  Finally, 
he  was  unacquainted  with  the  theoretically  important  occurrence  of 
the  Kupferschiefer  in  Bohemia.  The  contemporaneous  origin  of  the 
ore  and  rock  at  Mannsfeld  was  with  him,  so  to  speak,  a  dogma,  as 
may  be  perceived  in  some  of  his  expressions  (op.  cit.,  p.  302) : 

"  The  local  ore-bearing  character  of  the  foot-  and  hanging-walls  of  the  Kupfer- 
schiefer-ked  is  no  proof  to  the  contrary,  for  it  is  always  confined  to  the  immediate 
neighborhood  of  the  bed."  (?) 

"  Into  the  sea,  rich  in  fishes  and  plants,  from  which  the  marly  slate  was  deposited, 
flowed  abundant  metallic  solutions,  which  killed  the  organisms  and  were  themselves 
reduced  by  the  products  of  decay."  (?) 

The  first  of  these  propositions  becomes  logical  if  it  is  simply  re- 
versed in  sense ;  and  the  bold  hypothesis  of  the  second  indicates  a 
doubt  which  the  author  is  seeking  in  this  way  to  set  at  rest.  His 
statement  (p.  302) : 

"It  is  not  to  be  doubted  that  metallic  sulphides  may  be  formed  at  the  earth's  sur- 
face, under  ordinary  pressure  and  temperature,  beneath  a  water-covering  which  ex- 
cludes the  air," 

is  quite  correct ;  but  when  he  adds : 

"And  there  is  therefore  nothing  to  prevent  the  belief  that  sulphuretted  ores 
could  be  precipitated  at  the  same  time  with  the  deposition  of  sedimentary  rocks," 

it  is  necessary  to  add,  "provided  the  metallic  salts  were  present  in 
the  sea-basin." 

This  is,  indeed,  the  center  of  gravity  of  the  whole  question  ;  and, 
as  I  have  shown,  the  proposition  presents  an  improbability. 


116  THE   GFNESIS    OF   ORE- DEPOSITS. 

Various  other  peculiarities  of  individual  ore-occurrences  are  cited 
iu  favor  of  the  theory  of  contemporaneous  origin  ;  but  all  of  them, 
when  impartially  weighed,  are  equally  consistent  with  a  different 
genetic  explanation,  and  fail  to  be  as  significant  as  the  Mannsfeld 
type  for  the  theory  in  question. 

The  Copper -Sandstones  of  Bohemia. — In  Bohemia  and  on  the  west 
slope  of  the  Urals,  the  copper  ores  of  the  Permian  strata  occupy  by 
no  means  a  continuous  horizon,  but  occur  as  impregnations  in  dif- 
ferent beds,  beside,  above,  or  below  one  another.  There  are  here, 
as  in  the  German  Kupferschiefer  mines,  fault-fissures  which  may 
have  served  as  ore-conduits;  and  in  these  regions  the  notion  of  a 
primary  sedimentary  origin  of  the  ores  has  not  been  so  often  sug- 
gested. At  some  places  in  Bohemia,  as,  for  instance,  at  Starken- 
bach,  melaphyres  appear  above  the  ore- beds. 

In  almost  all  these,  as  in  many  of  the  German  deposits,  the  cop- 
per sulphides,  especially  redruthite,  occur  in  the  neighborhood  of 
plant-remains;  and  oxidized  copper-ores  predominate,  as  a  rule,  in 
the  ore- beds  in  sandstone. 

Not  only  Permian,  but  also  Triassic  and  still  more  recent  sand- 
stones, exhibit  analogous  deposits,  containing  lead,  silver,  and  anti- 
mony, as  well  as  copper.  At  Boleo,  in  Lower  California,  such  an 
ore-deposit  is  known  in  Tertiary  strata.  The  range  of  illustration!?, 
therefore,  is  an  extensive  one.  I  can  mention  but  a  few. 

St.  Avoid. — Concerning  the  copper-ores  in  the  Triassic  sandstone 
of  St.  Avoid  and  Wallerfangen,  Groddeck  gives  (p.  90)  a  brief  de- 
scription, based  on  an  article  by  C.  Simon.*  The  sporadic  ores  are 
most  abundant  in  the  vicinity  of  fault-fissures ;  but  only  single 
strata  are  rich,  while  other  porous  layers  near  by  are  barren  of 
ore.  The  ores  extend  in  zones,  independent  of  the  course  of  the 
fissures,  which  they  often  even  cross  at  right-angles.  These  two 
features  are  said  to  prove  the  contemporaneous  origin  of  the  ore  and 
rock,  "  since  the  enrichment  of  a  zone  where  it  is  cut  by  the  fissures 
can  be  simply  explained  by  the  leaching-out  of  ores  in  higher  strata, 
and  their  re-deposition  in  or  near  the  fissure."  I  must  confess  that 
this  explanation  is  not  satisfactory  to  me.  Figs.  80  and  81  illustrate 
the  situation. 

At  Bleiberg,  in  St.  Avoid,  concretions  of  galena,  of  pea-size,  oc- 
cur in  the  sandstone ;  and  below  the  same  layer  considerable  masses 
of  solid  galena  are  encountered. 

*  Berg  u.  H.  Ztg.,  1866,  p.  412. 


THE   GENESIS   OF   GEE-DEPOSITS.  117 

The  Lead- Deposit  of  Mechernieh,  near  Commern.* — This  deposit  has 
a  special  interest  in  this  connection,  since  it  consists  of  sandstone  of 
considerable  thickness,  somewhat  porous,  and  impregnated  with  small 
concretions  of  galena  (Knoten),  which  have  often  been  considered  as 
contemporaneous  in  deposition  with  the  rock.  The  district,  situated 
on  the  north  edge  of  the  Eifel  Mountains,  embraces  a  zone  about  7 
kilometers  (4J  m.)  long,  through  Call,  Keldenick,  Mechernich,  and 
Strempt.  Already  in  the  Roman  period,  at  the  Tanz  Mountain, 
near  Keldenick,  mining  was  done  upon  galena  veins  in  the  Devonian 
limestone,  which  is  overlain  by  the  sandstone  and  conglomerate  of 
the  variegated  sandstone  formation.  The  conglomerate  covering  the 
sandstone  has  the  name  of  Wackendeckel,  and  sometimes  carries  ore, 
the  cement  between  its  pebbles  being  traversed  by  galena  and  oxi- 
dized products,  especially  cerussite,  which  were  formerly  mined. 

It  is  at  present  the  sandstone,  impregnated  with  galena  concretions 
(Knoten)  to  the  extent  of  5  to  30  kg.  (0  5  to  3  per  cent.)  of  lead,  and 
1  to  6  grammes  (0.03  to  0.18  oz.  Troy)  silver  per  metric  ton  of  2204 
pounds,  which  is  the  principal  basis  of  an-extensive  mining  industry. 

The  thickness  of  this  Knotensandstein,  the  number  of  its  inter- 
calated conglomerate  layers,  and  the  richness  in  ore  of  each  stratum 
vary  greatly,  as  do  also  the  number,  direction  and  manner  of  throw 
of  the  fault-fissures  by  which  it  is  traversed.  Fig.  82,  represent-' 
ing  the  stratigraphy  SW.  of  the  boundary  of  the  mining  grant  at 
Meinerzhagen,  shows  the  irregularity  of  the  displacements.  Within 
the  grant,  the  several  JTnofen-layers  are  united  into  a  single  bed, 
about  22  meters  (72  feet)  thick,  separated  by  a  conglomerate  layer 
from  the  Devonian  rocks  below,  and  overlain  by  another  conglom- 
erate, the  so-called  Wacltendeckel,  above  which  is  the  barren  red 
sandstone.  In  general  terms,  there  lies  here  upon  an  impermeable 
floor  a  pervious  group  composed  of  sandstones  and  conglomerates, 
overlain  by  argillaceous  red  sandstone  and  loam. 

The  Knoten,  never  larger  than  peas,  exhibit,  when  prepared  in 
thin  sections  and  mounted  in  Canada  balsam,  crystalline  aggre- 
gates of  galena,  in  which  the  crystal-faces  are  turned  outwards,  away 
from  the  center;  that  is,  they  are  by  no  means  composed  of  spherical 
masses,  as  they  seem  to  the  naked  eye  to  be,  when  examined  as 

*  Banr,  "  Das  Vorkornmen  von  Bleierzen  am  Bleiberge  bei  Commern,"  Esch- 
weiler  Pumpe,  1859. 

F.  W.  Huperts,  Der  Bergbau  u.  Huttenbetrieb  des  Mechernicher  Bergw.  akt.  Vereins, 
Koln,  1883. 

Ellsworth  Daggett,  "The  Lead  and  Silver  Works  of  the  Mecheruich  Mining 
Company,"  E.  and  M.  J.,  xxiii. 


118  THE   GENESIS   OF   ORE-DEPOSITS. 

they  come  from  the  crumbly  rock.  Their  distribution  in  the  sand- 
stone generally  follows  the  bedding;  but  in  the  neighborhood  of 
the  cross-faults  I  observed  an  accumulation  of  Knoten  in  zones  par- 
allel to  these  steep  fissures.  Moreover,  I  found  occasionally  in  the 
fissures  themselves  threads  of  galena  and  pyrite;  and  hence  I  do  not 
doubt  that  the  ore-deposition  here  was  secondary,  and  proceeded 
from  the  fissures.  To  gain  a  clear  view  of  this  question,  it  is  neces- 
sary to  include  the  ore-occurrence  in  the  conglomerates,  where,  as 
already  observed,  it  impregnates  the  material  cementing  the  pebbles, 
and  also,  the  nearest  ore-occurrence  in  the  Devonian  limestone, 
where  it  appears  in  fissure- veins. 

In  my  opinion,  the  loose,  pervious  sandstone,  enclosed  between 
less  permeable  strata,  and  cut  by  many  fault- fissures,  was  impreg- 
nated by  ascending  springs,  which  employed  it  as  a  path  in  their 
circulation;  but  it  cannot  be  determined  what  constituted  the  centers 
around  which  the  galena  concretions  are  formed.  May  it  have 
been  minute  particles  of  feldspar,  such  as  are  still  occasionally  visi- 
ble; or  was  it  organic  substances,  which  have  now  entirely  disap- 
peared ? 

Freihung. — Perhaps  additional  hints  may  be  furnished  bv  the 
mines  of  Freihung  in  the  Bavarian  Upper  Palatinate,  which  Cotta 
considers  analogous  to  those  of  Mechernich.  Here  galena  and  cer- 
ussite  impregnate  the  Keuper  sandstone,  the  steep  dip  of  which  they 
share.  At  the  Nuremberg  Exposition  of  188'2,  maps,  ore-  and  rock- 
specimens  from  the  mines  of  the  Bavarian  Lead-Mining  Co.  were 
exhibited.  Fig.  83  is  a  section  through  the  Vesuvius  mine.  I  was 
struck  with  numerous  specimens  of  tree-stems  changed  to  galena; 
and,  coming  subsequently  into  possession  of  such  a  specimen,  I  had 
a  polished  section  prepared  from  it.  The  pieces  of  these  stems  ex- 
hibited are  about  20  centimeters  (8  inches)  long,  and  elliptical  in 
sections,  say  5  to  7  by  10  to  15  centimeters  (2  to  3  by  4  to  6  inches.) 
The  fiber  and  the  annual  rings  could  be  recognized  on  the  surfaces 
of  fracture,  but  were  extremely  plain  in  the  polished  section.  In- 
deed, they  were  indicated  by  the  cleavage  of  the  specimens.  I  have 
thin  slivers,  2  to  4  mm.  (0.08  to  0.16  inches)  in  diameter  and  several 
centimeters  long,  representing  the  fibers  of  the  original  wood.  The 
former  bark  is  replaced  by  a  zone  of  first  pyrite,  and  then  quartz 
grains  cemented  with  pyrite.  I  do  not  know  that  the  determination 
of  the  species  of  the  wood  has  been  attempted,  but  I  think  it  should 
be  approximately  practicable.  Fig.  84  is  a  diagram  of  the  section 
of  such  a  stem  altered  to  galena. 


THE   GENESIS   OF   ORE-DEPOSITS.  119 

Certainly  we  have  here  another  instance  showing  that  the  organic 
substance  attracted  metallic  solutions  and  reduced  them  to  sulphides, 
and  this,  under  conditions  similar  to  those  of  Mechernich.  The 
latter  occurrence  may,  therefore,  be  most  simply  explained  by  the 
hypothesis  of  an  organic  substance,  distributed  through  the  rock, 
which  reduced  the  circulating  mineral  solutions  and  occasioned  the 
formation  of  the  concretions  (Knoten). 

Silver  Reef. — Accustomed  as  we  are  to  find  silver  associated  with 
lead-ores,  we  are  surprised  by  the  occurrence,  in  the  Silver  Reef 
district  of  Utah,  in  probably  Triassic  sandstones,  of  silver  accom- 
panied by  copper.  So  far  as  can  be  gathered  from  the  various 
descriptions  at  hand,*  there  occur  here  two  beds  (the  outcrops  of 
which  are  called  "reefs"),  which  carry  silver,  either  exclusively  or 
with  a  little  copper — the  former  usually  as  a  chloride,  but  some- 
times native;  and  the  latter  in  the  ordinary  oxidized  ores.  It  may 
be  reasonably  inferred  that  the  deposit  has  been  thus  far  exposed  in 
its  upper,  chloridized,  and  oxidized  zones ;  and  that  in  depth  it 
would  be  found  to  contain  sulphide-ores.  Whether  such  depth  has 
been  reached  by  the  miners  I  do  not  know. 

The  beds  consist  of  red  and  gray  argillaceous  sandstones  and 
arenaceous  clay-slates,  between  the  Iamina3  and  in  the  cross-joints  of 
which  the  ores  occur,  being  the  more  concentrated,  the  more  highly 
fissured  the  condition  of  the  rock.  Although  traces  of  silver  are 
found  throughout  the  bed,  the  pay-ore  is  confined  to  separate  chim- 
neys or  channels,  which  descend  on  the  true  dip,  or  pitch  obliquely 
to  it.  The  richest  bodies  are  said  (Rolker,  L  c.,  p.  25)  to  be  most 
frequently  found  above  a  certain  thin,  very  clayey,  sandstone 
stratum.  Very  often,  but  not  always,  the  silver-ore  is  accompanied 
by  carbonized  vegetation,  such  as  trunks  and  stems  of  trees,  and 
reed-like  plant-remains,  which  are  covered  and  impregnated  with 
horn-silver.  The  copper-  and  silver-  ores,  while  occurring  to  a 
certain  degree  in  association,  seem  to  exclude  one  another,  and  are 
seldom  found  in  actual  mixture. 

The  same  sandstone  which  here  carries  ore  is  said  to  be  repre- 
sented in  the  plateau  cut  by  the  Colorado  river;  but  there  the  strata 

*  "  The  Silver  Reef  District,  Southern  Utah,"  (by  R.  P.  Rothwell  or  Thomas 
Couch  ?),  Eny.  and  M.  Jour.,  xxix.,  pp.  25,  45,  59,  79,  351. 

C.  M.  Rolker,  "The  Silver-Sandstone  District  of  Utah,"  Tmm.  A.  I.  M.  E.,  ix, 
21. 

J.  S.  Newberry,  "  Report  of  the  Stormont  Silver  Mining  Co.,"  E.  and  M.  J., 
xxx.,  p.  269. 


120  THE   GENESIS   OF  ORE- DEPOSITS. 

are  horizontal  and  undisturbed,  whereas  in  the  ore-district  they  dip 
rather  steeply,  are  much  disturbed,  and  are  in  many  places  covered 
with  eruptive  rocks,  including  basalt.  This  neighborhood  to  erup- 
tives  renders  it  probable  that  here,  as  in  so  many  other  places  in 
Western  America,  the  ores  have  been  introduced  by  the  mineral 
springs  which  usually  follow  eruptive  activity.  Rothwell,  Couch, 
and  Rolker  are  of  this  opinion;  whereas,  Newberry  is  inclined  to 
suppose  a  contemporaneous  origin  of  ores  and  rock.  The  principal 
arguments  for  his  view  are,  the  alleged  great  area  of  silver-bearing 
Triassic  strata  in  that  region  ;  and  the  circumstance  that  the  richest 
bedded  and  lenticular  ore-bodies  are  enclosed  in  almost  impermea- 
ble slate-clays,  which  would  not  have  permitted  a  subsequent  en- 
trance of  the  mineral  solutions.  Neither  of  these  statements  dis- 
proves the  secondary  origin  of  the  ores.  They  could  have  been 
deposited  in  any  given  way  on  a  large  scale,  as  well  as  a  small  one  ; 
and  that  the  almost  impermeable  slate-clays  did  not  prevent  the 
entrance  of  solutions  is  proved  by  the  subsequent  alteration  of  the 
original  filling  to  chlorides  and  oxides.* 

Moreover,  the  deposits  are  not  regular  strata  but  chimneys  and 
channels  in  parts  of  strata,  and  this  character,  which  they  possess  in 
common  with  so  many  other  deposits,  should  be  decisive  in  favor  of 
their  secondary  origin — a  conclusion  which,  in  my  opinion,  is  always 
reached  when  observations  are  not  confined  to  single  localities,  but 
extended  over  whole  series  of  analogous  phenomena. 

Copper- Deposits  of  New  Mexico  and  Arizona. — Traces  of  si  milar  ore- 
distribution  in  sandstones  seem  to  be  not  infrequent  in  the  American 
West.  Thus  F.  M.  F.  Cazinf  says  of  the  copper-ores  of  the*  proba- 
bly Triassic  sandstones  of  the  Nacimiento  mountains  in  N.  W.  New 
Mexico,  which  J.  S.  Newberry  had  described  in  1860: 

"The  ore  occurs  nearly  exclusively  as  the  petrefaction  of  the  leaves,  stems,  limbs 
and  trunks  of  palms.  Frequently  the  ore  is  coated  with  a  film  of  jet  or  coal.  It  is 
always  easily  separated  from  the  rock.  The  ore  is  predominantly  erubesite,  cop- 
per-glance and  melaconite,  and  it  appears  to  be  distributed  all  over  the  massive 
stratum,  but  is  more  densely  collected  on  seams  and  cleavages,  in  some  instances 
forming  a  single  layer  of  petrified  parts  of  palm-wood." 

This  occurrence,  which  is  analogous  to  those  in  Bohemia  and  in 

*  Compare  F.  M.  F.  Cazin,  ''The  Origin  of  Copper-  and  Silver-Ores  in  Triassic 
Sandrock,"  E.  and  M.  J".,  xxx.,  p.  381. 

f  "  New  Mexico  vs.  Lake  Superior  as  a  Copper-Producer." — E.  and  M.  J.,  xxx  , 
pp.87,  108. 


THE   GENESIS   OF   OKE-DEPOSITS.  121 

the  province  of  Perm,  was  declared  to  possess  great  economic  im- 
portance. Its  later  developments  are  not  known  to  me. 

W.  P.  Blake*  has  described  an  analogous  occurrence  in  the  sand- 
stones and  conglomerates  overlying  the  granites  in  Copper  Basin, 
Yavapai  county,  Arizona,  where  the  copper-ores  are  found  uncon- 
nected with  any  organic  substances.  In  the  underlying  granite, 
however,  there  are  fissures  filled  with  copper-ores.  He  thinks  it 
probable  that  copper  sulphides  circulating  in  the  highly  permeable 
sandstone  were  precipitated  as  carbonate  by  carbonate  of  soda,  while 
the  resulting  sulphate  of  soda  escaped  in  solution,  to  be  concentrated 
by  evaporation,  forming  deposits  of  thenardite,  which  is  common  in 
Arizona. 

Lower  California. — At  Boleo,  opposite  Guaymas,  on  the  peninsula 
of  Lower  California,  E.  Fuchsf  has  described  a  remarkable  deposit 
of  copper-ores  in  Tertiary  sandstones,  conglomerates  and  tufas,  which 
must  be  mentioned  under  this  head.  The  east  slope  of  the  (mostly 
eruptive)  mountain  range  extending  through  the  peninsula  is  a 
plateau,  gently  descending  towards  the  Gulf  of  California,  and  cut 
by  precipitous  canons.  It  is  formed  of  strata  containing  character- 
istic Miocene  fossils.  Tufas  decidedly  predominate,  and  the  series 
contains  three  or  four  copper-bearing  beds,  covering  a  large  area, 
and  out-cropping  at  many  places  in  the  cations.  These  lie  imme- 
diately upon  conglomerates  of  pebbles  of  eruptive  rock  (different 
and  characteristic  for  each  horizon)  and  are  overlain  by  clayey  tufas. 
The  whole  is  traversed  by  several  fissures,  of  which  the  largest  and 
most  important  is  a  fan  It- fissure,  occurring  at  the  western  border  of 
the  district  and  striking  about  parallel  with  the  sea-shore. 

In  the  ore-beds  above  the  ground-water  level,  disseminated  oxi- 
dized ores  prevail,  such  as  black  oxide  of  copper,  and  the  protoxide, 
with  atacamite  (CuCl  -f-  3  CuO  -f-  3II2O),  azurite,  malachite  and 
chrysocolla,  with  crednerite  (2  Mn2O3,  3  CuO).  In  the  second  ore- 
bed  (counting  downwards)  there  are  peculiar  globular  concretions, 
like  oolites,  of  copper  oxide  and  carbonate,  sometimes  several  centi- 
meters in  diameter,  which  are  locally  called  boleos,  whence  the  name 
of  the  district.  Though  greatly  interested  in  this  type  of  ore,  I 
have  never  succeeded  in  getting  specimens,  and  am  unable  to  form 


*  "The  Copper- Deposits  of  Copper  Basin,  Arizona,  and  their  Origin." — Trans 
A.  I.  M.  E.,  xvii.,  479. 

f  "  Note  snr  les  Gisements  de  Cuivre  da  Boleo." — Assoc.  Francaise  pour  VAvan- 
cement  des  Sciences,  1885. 


122  THE   GENESIS   OF   ORE-DEPOSITS. 

from  the  hasty  description  of  Fuchs  a  clear  conception  as  to  its 
genesis. 

The  third  bed  lies  in  part  below  the  ground-water  level,  and  con- 
tains, in  addition  to  the  foregoing  minerals,  the  copper  sulphides 
chalcosine  (Cu2S)  and  covelline  (CuS). 

The  ore-beds  are  composed  of  tufa  (the  slime,  according  to  Fuchs, 
of  volcanic  eruptions),  in  which  ores  in  disseminated  spots  and  vein- 
lets  ("  sous  forme  demouche  oude  veinules"),  as  well  as  globular  con- 
cretions, are  irregularly  distributed,  with  a  visible  tendency  to  con- 
centrate towards  the  bottom  of  the  bed,  where  they  form  a  compact 
ore-layer,  15  to  25  centimeters  (6  to  10  inches)  thick. 

With  regard  to  genetic  questions,  we  must  bear  in  mind  that  the 
fossils  found  in  these  strata  indicate  an  open  though  not  very  deep 
sea;  it  is,  therefore,  impossible  to  assume  that  iron-,  manganese-  and 
copper-ores  were  dissolved  in  it,  and  were  precipitated  from  it  at  the 
same  time  with  the  rock.  A  periodical  metallic  precipitation,  three 
or  four  times  repeated,  in  an  open  marine  basin,  is  out  of  the  ques- 
tion ;  and  we  are  forced  in  this  case,  even  more  strongly  than  else- 
where, to  assume  a  secondary  origin  for  the  ores.  The  data  neces- 
sary for  its  explanation  «are  still  wanting,  but  can  undoubtedly  be 
secured  by  the  further  advance  of  mining  work.  E.  Fuchs  con- 
tented himself  with  pointing  out  the  after-effects  of  eruptive  pro- 
cesses, and  did  not  enter  upon  the  genetic  question.  Certainly  the 
conglomerates  underlying  the  ore-bed  must  have  played  an  impor- 
tant part,  representing,  very  likely,  the  channels  through  which  the 
mineral  solutions  ascended,  to  be  reduced,  probably  by  the  presence  of 
organic  matter,  in  the  tufas  above. 

b.  Metasomatio  Deposits  in  Soluble  Rocks. 

A  metasomatic  replacement  of  the  original  rock-material  was 
clearly  proved  long  ago  for  some  instances — e.g.,  calami ne-deposits — 
while  in  other  cases,  where  proof  has  not  been  obtained,  analogies 
in  the  observed  circumstances  speak  for  such  an  origin.  Parts  of 
such  deposits,  it  is  true,  may  be  fillings  of  spaces  of  dissolution, 
rendered  unrecognizable,  as  such,  by  the  absence  of  clearly-defined 
crustification  in  the  ore- precipitates.  We  must  accustom  ourselves 
to  the  fact  that  for  many  deposits,  not  yet  closely  enough  studied,  it 
is  impossible  to  determine  positively  the  mode  of  genesis,  and  we 
must  often  choose  provisionally,  of  the  two  modes  just  named,  the 
one  which  appears  to  represent  better  the  given  data. 

Calamine- Deposits. — The  calamine-depositsof  Raibl  in  Carinthia, 


THE   GENESIS   OF   ORE-DEPOSITS.  123 

Wiesloch  in  Baden,  Vieille  Montagne,  with  its  vicinity,  in  Belgium 
and  Germany,  and  other  places,  furnish,  in  the  fossils  of  the  lime- 
stone which  have  been  transformed  into  calamine,  the  clearest  proofs 
of  a  metasomatio  replacement  of  the  carbonate  of  lime  by  carbonates 
and  silicates  of  zinc.  Moreover,  the  structure  and  form  of  the  ore- 
deposits  is  characteristic  of  this  origin,  these  being  mostly  bodies  of 
irregular  outline,  with  portions  projecting  far  into  the  country-rock. 
Often  the  progress  of  the  replacement  can  be  traced.  Thus,  at 
Raibl  (Fig.  85),  in  places  where  the  process  has  started  from  seams, 
the  gradual  advance  from  the  seam  into  the  rock  may  be  observed  ; 
the  outermost  portions  being  relatively  the  most  recent,  and  lying 
against  a  peculiarly  uneven,  rough  surface  of  limestone. 

Sometimes  features  of  the  original  rock-structure  are  repeated  in 
calamine,  as,  for  instance,  the  cellular  structure  of  the  so-called 
Rauchwacke  (the  cargneule  of  the  Swiss  geologists),  which  consists 
of  a  skeleton  of  thin,  smooth  lime-partitions,  from  among  which  the 
limestone  has  been  in  part  dissolved  away,  or  left  only  in  separate 
decomposed  splinters.  This  is  evidently  the  result  of  a  very  com- 
plex metamorphosis,  which  Groddeck  has  observed  also  in  the 
quicksilver-deposit  of  Avala  in  Servia.  The  cell- walls,  which 
represent  the  fillings  of  cracks  in  a  shattered  limestone,  have  been 
subsequently  changed  to  calamine,  and  covered  with  botryoidal 
clusters  of  that  mineral  (Fig.  86). 

Calamine  is  frequently  formed  by  atmospheric  agencies  above  the 
ground-water  level,  and  is  a  frequent  accompaniment  of  lead-  and 
zinc-deposits  in  limestone. 

Space  does  not  permit  the  description  here  of  the  manifold  deposits 
in  Belgium,  Rhenish  Prussia,  Westphalia,  Upper  Silesia,  Sardinia, 
Algiers,  etc.,  which  are,  moreover,  not  known  to  me  by  personal 
observation.  The  text-books  of  Cotta,  Groddeck  and  Phillips  give 
some  account  of  them,  and  refer  to  sources  of  more  detailed  informa- 
tion. 

Laurium. — It  is  only  in  recent  periods  that  the  features  of  the 
extensive  mining  region  of  Laurium  in  Greece,*  worked  two  thou- 
sand years  ago,  have  been  described.  Although  various  kinds  of 
deposits  are  represented,  most  of  them  belong  under  the  present 
head. 

In    the   Camaresa  district,  a  series  of  nearly   horizontal,  non- 


*  A.  Cordelia,  La  Gr&ce  sous  le  Rapport  Geologique  et  Min'eralogique,  Paris,  1878 ; 
and  Le  Laurium,  Marseilles,  1869.  A.  Huot,  Rapport  sur  les  Mines  du  Sumium, 
1880,  and  Memoires  de  la  Societt  des  Ing.  Civ.,  1876-78. 


124  THE   GENESIS   OF   ORE-DEPOSITS. 

fossil iferous  limestones  and  crystalline  schists  is  cut  by  a  number  of 
eruptive  dikes,  and  suddenly  assumes  on  the  NE.  a  steep  dip, 
probably  indicating  a  considerable  dislocation.  The  whole  group  is 
traversed  by  a  number  of  ore-veins,  which,  in  the  schists,  are  often 
rich  enough  to  pay  for  mining.  But  the  main  mass  of  the  ores  lies 
on  the  contact  between  limestone  and  schist,  and  extends  into  the 
former  in  separate  bodies  or  shoots.  At  the  so-called  second  and 
third  contacts,  the  bodies  have  a  prevailing  funnel-shape  and  a 
vertical  position.  Fig.  87,  an  illustration  from  Htiot,  shows  the 
apexes  of  the  funnels  to  point  on  one  contact  upward,  and  on  the 
other  downward — but,  in  either  case,  into  the  limestone,  according 
as  it  overlies  or  underlies  the  schist.  The  first  form  may  be  ex- 
plained by  the  pressure  of  the  ascending  solutions.  The  second,  as 
shown  in  this  figure,  is  perhaps  somewhat  ideally  sketched  ;  at  least 
the  sections  of  this  third  contact  given  by  Cordelia  show  ore-bodies 
following  the  contact-plane  itself. 

According  to  Fig.  88  (also  from  Huot)  the  ore-bodies  are  funnel- 
shaped  in  N.  to  S.  section,  but  from  E.  to  W.  have  a  flat  westward 
pitch,  which  is  hard  to  explain  unless  it  represents  some  kinds  of 
cleavage  parallel  to  the  dislocation  already  mentioned.  Below  the 
second  contact,  which  carries  chiefly  lead,  there  are  (at  the  Jean 
Baptiste  shaft,  for  instance,  according  to  Cordelia)  great  masses  of 
calami  ne.  the  secondary  origin  of  which  from  zincblendeis  doubtful, 
since  it  would  involve  the  assumption  that  the  ground-water  zone 
had  extended  to  this  depth.  As  to  the  present  subterranean  water- 
level,  I  find  in  the  descriptions  at  hand  only  the  statement  that  the 
region  generally  is  very  dry,  and  tint  the  ancients,  who  mined  to 
the  depth  of  120  meters  (394  feet)  had  no  water  to  hoist.  With 
regard  to  the  structure  of  the  galena-deposits,  I  may  say  that  I  saw 
in  the  exhibit  of  the  Cie  Frangaise  des  Mines  de  Laurium,  at  the 
Paris  Exposition  of  1867,  masses  of  galena,  blende  and  pyrite  show- 
ing distinct  stratification,  but  did  not  learn  from  which  deposit  they 
came. 

Which  of  the  various  eruptive  rocks  of  the  district  (eurite, 
porphyry,  diabase,  serpentine,  trachyte)  gave  occasion  for  the  ascend- 
ing springs  which  brought  up  the  ore,  cannot  as  yet  be  determined. 

The  minerals  accompanying  the  products  of  decomposition  in  such 
deposits,  particularly  of  calamine,  are  naturally  often  limonite  and 
other  ores  of  iron.  In  many  countries  these  play  an  independent 
part,  being  often  formed  by  the  metasomasis  of  limestone,  as  proved 
by  the  irregular  masses  of  the  deposits  and  the  contained  fossils 
transformed  into  ore. 


THE   GENESIS   OF   ORE-DEPOSITS.  ]  25 

Alsace. — An  instance  is  furnished  by  the  so-called  Bolmeiscnerze 
of  Alsace  and  adjacent  regions  which  have  been  described  and  cor- 
rectly explained  by  Daubree.* 

At  Liebfrauenberg,  irregular,  lean  beds  of  this  character,  com- 
posed principally  of  limonite,  but  scarcely  workable  with  profit,  lie 
on  both  sides  of  an  anticlinal  of  Vosges  sandstone,  and  are  covered 
with  alluvium.  In  one  place,  however,  near  Goersdorf,  an  un- 
decomposed  body  of  pyrite  and  mispickel  occurs  instead  of  lim- 
onite. 

Cumberland. — In  Cumberland,  limonite-deposits  occur  on  the  con- 
tacts of  the  Carboniferous  Mountain  limestone,  both  with  the  over- 
lying millstone  grit  and  with  the  underlying  Silurian  schists. 
They  are  connected  with  fault-fissures,  on  both  sides  of  which 
they  appear,  as  is  shown  in  Fig.  89,  taken  from  a  paper  by  Mr* 
J.  D.  Kendall.f 

Carniola. — The  Alps  offer  some  remarkable  examples  of  Bohnei- 
senerze.  These  occur,  according  to  A.  von  Morlot,J  in  the  region  of 
Wochein  in  Carniola  (known  for  its  iron-ores  and  bauxite)  in  the 
dolomite  and  limestone  mountains  only,  and  either  in  the  form  of  beds 
under  the  dolomite  detritus,  or  in  clay,  in  the  caverns  of  the  dolo- 
mite. Fig.  90  is  a  section  showing  the  latter  form.  In  this  case 
the  flatter-lying  cavern  was  partly  filled  with  lime-detritus  and  clay 
up  to  its  connection  with  a  higher  vertical  cavern,  while  the  latter  was 
filled  with  Eohnerze  enclosed  in  loam,  and  had  been  mined,  according 
to  Morlot,  to  the  considerable  depth  of  250  meters  (820  feet).  Here 
and  there  a  nucleus  of  pyrite  is  found  in  the  iron-ore.  The  beds 
and  mass-deposits  of  bauxite  associated  with  limonite  sometimes  show 
also  the  "  bean-structure." 

c.  Deposits  in  Crystalline  Schists  and  Eruptive  Rocks. 

Without  entering  here  upon  a  discussion  of  the  subject  of  regional 
metamorphosis,  I  may  remark  that,  as  a  general  rule,  the  older  a  rock 
is,  the  more  changes  it  will  be  found  to  have  undergone  ;  yet  that 
these  changes  do  not  advance  in  all  places  uniformly.  Many  Creta- 
ceous and  Tertiary  formations  of  the  Alps  present  a  highly  meta- 
morphosed, and  therefore  ancient,  appearance;  while  many  Silurian 
formations — as,  for  instance,  that  which  surrounds  St.  Petersburg — 

*  Les  Eaux  Souterraines  aux  fyoques  Anciennes,  p  79. 
f  Trans.  N.  of  E.  Jnst.  of  M.  E.,  1878,  vol.  xxviii.,  pi.  xxviii. 
J  "Geol.  Verhaltn.  von  Ober-Krain,"  Jahrb.  d.  k.  k.  Geol.  #.  A.,  i.,  1850,  p. 
407. 


126  THE   GENESIS   OF   ORE-DEPOSITS. 

have  been  so  little  altered  that  the  fossil  shells  which  they  contain 
still  have  the  mother-of-pearl  luster.  Some  regions,  in  a  word,  have 
been  more  strongly  attacked  than  others,  through  causes  which  we 
will  not  here  pause  to  consider;  and  when  we  follow  the  stratified 
groups  downward,  we  come  upon  the  various  crystalline  schists  often 
traversed  by  eruptives,  and  showing  no  longer  any  trace  of  the  clastic 
sediments,  which  have  been  wholly  transformed  to  crystalline  masses. 
We  cannot  hope  to  find  petrified  organisms  in  these  masses;  but  the 
occurrence  of  disorganized  organic  material  in  the  form  of  anthracite 
and  graphite  proves  that  at  the  time  the  rocks  were  formed,  organic 
life  must  have  been  represented  in  the  sediments. 

Many  indications,  available  in  the  distinctly  sedimentary  rocks  as 
guides  in  the  determination  of  the  relative  age  of  their  ore-deposits, 
are  here  wanting.  The  bedding  becomes  more  and  more  obscure, 
and  is  sometimes  no  longer  distinguishable  from  the  cleavage.  Many 
of  the  ore-deposits  in  these  rocks  have  also  become  in  whole  or  part 
crystalline,  adjusting  themselves  to  the  prevailing  stratification  or 
cleavage,  so  that  most  of  them  present  a  bed-like  structure  and  form. 
Whoever  believes  in  the  possibility  of  a  contemporaneous  formation 
of  the  ores  with  the  rocks  will  not  trouble  himself  here  with  genetic 
speculations,  but  will  see  in  these  deposits  simply  "ore-beds,"  accord- 
ing to  the  old  classifications. 

Taberg,  Sweden. — The  circumstance  that  magnetite  is  a  constitu- 
ent of  many  eruptive  rocks  has  inclined  many  geologists  to  regard 
masses  of  magnetite  in  the  neighborhood  of  such  rocks  as  imme- 
diately belonging  to  them.  This  theory  originated  in  connection 
with  the  Taberg  deposit,  in  Smaland,  Sweden,  and  was  propagated 
by  F.  L.  Haussmann,*  W.  Hissinger,f  and  A.  Daubree  ;|  and 
Taberg  has  been  regarded  ever  since  as  an  example  of  the  primitive 
existence  of  magnetite-deposits,  those  of  Kackanar,  Visokaya  Gora, 
and  Blagodat  being  classed  with  it. 

The  question  arises,  where  the  line  is  to  be  drawn  between  an 
eruptive  rock  containing  magnetite  and  a  magnetite  deposit.  An 
eruptive  rock,  like  that  of  Samokov,  in  the  Pils  mountains  in  Bul- 
garia, from  the  weathered  detritus  of  which  magnetite  is  obtained 
by  ore-dressing,  is  not  properly  an  ore-deposit ;  but,  on  the  other 
hand,  that  of  Taberg,  where  the  ore  is  not  only  finely  disseminated 

*  Reise  durch  Skandinavien,  Gottingen,  18U-1S,  i.,  p.  165. 

f  Versuch  einer  mineralog.  Geographic  von  Schweden  (Woehler's  translation),  1826, 
p.  205. 

I  ScandinaviensErzlagerslatten  (edited  by  G.  Leonhard),  Stuttgart,  1846,  p.  25. 


THE   GENESIS   OF  ORE-DEPOSITS.  127 

in  large  amount,  but  also  occurs  in  separate,  solid  veins,  may  fairly 
be  so  called.  According  to  A.Sjogren,*  the  rock  consists  of  olivine, 
magnetite,  and  a  little  plagioklase,  with  mica  and  apatite  as  acces- 
sories. In  other  words,  it  is  an  already  metamorphosed  rock. 
Considering  that  at  several  places  in  Scandinavia  magnetite  occurs 
in  the  crystalline  schists  also,  it  seems  unlikely  that  the  magnetite 
of  Taberg  belongs  to  the  primitive  rock.  This  is  confirmed  by  the 
observation  of  Th.  Kjerulf,  that  all  the  ore-deposits  of  Norway 
follow  the  courses  of  eruptive  rocks.  Taberg  will  scarcely  prove  to 
be  an  exception,  and  may,  therefore,  be  regarded  as  a  secondary  or 
xenogenous  ore-deposit. 

Before  proceeding  further  I  must  mention  the  action  of  the 
mineral  solutions  upon  the  country-rock  of  some  veins,  which 
might  be  also  classed  as  impregnation.  In  this  respect  tin-deposits 
are  most  interesting,  because  they  carry  ore,  not  only  in  the  space 
of  discission,  i.e.,  the  vein-fissure,  but  to  a  large  extent  in  the 
neighboring  country-rock  also.  If  the  veins  occur  in  granite,  this 
is  changed  for  a  certain  width  into  greisen,  i.e.,  it  is  robbed  of  its 
feldspar,  which  is  even,  in  some  cases,  replaced  by  cassiterite  and 
associated  minerals.  Thus  are  formed  the  beautiful  pseudomorphs 
of  cassiterite  after  feldspar,  which  adorn  many  mineral  collections. 
(See  Fig.  91.) 

Figs.  91-93  are  taken  from  C.  LeNeve  Foster,  f  Fig.  91  repre- 
sents the  alteration  of  the  granitic  country-rock  to  greisen  on  both 
sides  of  a  fissure,  which  is  here  filled  with  symmetrical  quartz- 
crusts,  to  the  central  druse  or  comb.  Often  such  fissures  occur 
close  together  ;  and  since  each  has  its  own  zone  of  greisen,  the 
result  is  a  Stockwerk,  constituting  a  metamorphosis  of  the  granite, 
and  formed  by  these  fissures. 

Cornwall. — In  the  slate  or  killas  of  the  Cornish  miners,  there  is 
often  a  disturbance  of  the  bedding  in  the  neighborhood  of  the 
fissure  (Fig.  92),  such  as  is  observed  in  connection  with  fault- 
fissures  elsewhere ;  but  in  this  case  the  capel,  or  adjacent  portion 
of  the  slate,  is  altered  chemically  also,  being  impregnated  with 
quartz  and  traversed  by  streaks  of  ore.  The  fissure  itself  is  filled 
with  quartz,  cassiterite,  chlorite,  pyrite,  and  fragments  of  the  capel. 
When  several  fissures  come  together,  the  result  is  somewhat  compli- 
cated, but  can  be  reduced  to  the  simple  case  just  described. 

*  Neues  Jahrb.f.  Mineralogie,  1876,  p.  434. 

f  "  Remarks  on  Some  Tin-Lodes  in  the  St.  Agnes  District,"  Trans.  Roy.  Geol. 
*oc.  of  Cornwall,  1877,  ix.,  PI.  III. 


128  THE    GENESIS    OF   ORE-DEPOSITS. 

Still  more  interesting  is  the  tin-deposit  of  East  Wheal  Lovell, 
described  by  the  same  authority.*  At  the  side  of  a  narrow  quartz 
vein  the  ores  occur  in  the  granite,  from  which  they  are  not  separated 
by  any  definite  boundary,  so  that  the  ore-body  is  an  almost  vertical 
shoot,  confined  to  the  neighborhood  of  the  fissure,  yet  lying  in  the 
country-rock.  It  is  clear  that  a  mineral  water  of  high  solvent 
power,  must  have  ascended  under  great  pressure,  in  order  to  bring 
about  such  effects  in  a  rock  ordinarily  regarded  as  insoluble.  Fig. 
93  shows  the  situation  of  one  of  these  ore-shoots  in  granite,  at  the 
East  Wheal  Lovell  mine. 

The  ore-deposits  in  metamorphous  and  eruptive  rocks  occur  espec- 
ially in  the  great  crystalline  northern  areas,  in  Scandinavia,  Canada, 
and  the  northeastern  United  States. 

Scandinavia. — In  Scandinavia,  the  science  of  ore-deposits,  like  that 
of  petrography,  has  had  a  comparatively  independent  development. 
Although  these  countries  have  been  often  visited  by  foreign  observ- 
ers, few  analogies  with  European  deposits  have  been  noted — chiefly, 
no  doubt,  because  of  the  peculiar  character  of  the  occurrences  exam- 
ined, but  also  partly  because  of  the  differing  standpoints  and  views 
of  native  observers.  In  recent  times  a  difference  of  interpretation 
has  developed  itself  between  the  Norwegian  and  the  Swedish  geolo- 
gists; and  the  former,  since  Kjerulf,  have  approached  more  nearly 
the  Continental  view. 

As  already  remarked,  Kjerulf  traces  all  the  ore-deposits  of  Nor- 
way to  the  filling  of  spaces  of  discission,  and  particularly  of  a  pecu- 
liar space,  produced  by  the  sliding  of  the  rock  along  a  bedding- 
plane,  and  locally  called  a  Lineal. 

With  respect  to  the  ore-filling,  he  points  out  that  the  occurrence 
of  the  ore-deposits  must  always  be  studied  on  the  large  scale,  and 
that  this  method  shows  the  ore-deposits  to  occupy  certain  lines, 
characterized  by  the  presence  of  eruptive  rocks. f  The  ores  appear 
chiefly  in  the  crystalline  schists,  but  also  in  traces  along  the  contact, 
and  sometimes  in  the  eruptive  rocks  themselves.  In  the  first  case, 
the  different  sulphides,  mostly  accompanied  with  quartz,  lie  parallel 
with  the  bedding  or  cleavage  of  the  rock,  and  thus  look  like  beds; 
but  their  secondary  origin  is  indicated  by  the  slickensides,  the  branch- 
ing of  the  deposits  and  other  signs.  Sometimes  it  is  made  evident 

*  C.  Le  Neve  Foster,"  Remarks  upon  the  Tin -Deposits  of  East  Wheal  Lovell," 
Trans.  Hoy.  Geol.  Soc.  of  Cornwall,  1876,  lx.,  PI.  II. 

f  Die  Geologic  des  sudl.  u.  mittl.  Norwegen  (authorized  German  edition,  by  Dr.  A. 
Gurlt),  Bonn,  1880,  pp.  81,  284,  293. 


THE   GENESIS   OF   ORE-DEPOSITS.  129 

by  the  course  of  the  ore-masses,  cutting  across  the  bedding  or  cleav- 
age. In  the  museum  at  Christiania  there  are  many  large  specimens 
of  the  ore,  some  of  which,  having  been  polished,  show  this  structure 
plainly.  Pictures  of  some  of  them  have  also  been  published  by 
Kjerulf.* 

In  this  connection,  the  primitive  ore-bearing  character  of  the 
Fahlbdnder  (so  often  cited  by  geologists  as  primary  ore-beds,  which 
enrich  the  veins  by  which  they  are  crossed)  is  entirely  denied  (I.  c., 
p.  323).  It  has  been  proved  that  the  ores  of  the  Modum  fahlbands 
are  connected  with  the  malakoliteand  the  augite-rock  which  intrudes 
in  "  lineal  "  form  between  the  steep  strata  of  quartz-schists.  Figs. 
94  and  95  are  intended  to  show  the  appearance  of  these  deposits, 
formerly  deemed  to  be  beds.  The  former  represents  a  specimen 
from  the  Kongens  mine  at  Roras,  and  the  latter  a  part  of  the  speci- 
men illustrated  by  Kjerulf,  from  the  Mug  mine  at  Trondhjem.  In 
the  former,  the  subsequent  entrance  of  the  ore  is  at  once  recognized. 
The  latter  appears  as  if  the  crystallization  of  the  minerals  had  taken 
place  after  the  ore-impregnation. 

Of  course,  the  political  boundary  does  not  divide  the  nature  of  the 
ore-deposits  of  the  Scandinavian  kingdoms.  Those  of  Sweden  are 
often  the  continuations  of  the  Norwegian.  The  crystalline  rocks  are 
here  peculiarly  developed,  and  have  also  been  peculiarly  named  by 
the  Swedish  petrographers.  In  the  Swedish  granulite,  for  instance, 
one  would  scarcely  recognize  its  Continental  namesake.  These  rocks 
are  not  in  general  so  coarsely  crystalline  that  their  constituent  min- 
erals can  be  distinguished  with  the  naked  eye.  Ttie  so-called  eurites 
are  still  finely  crystalline,  and  the  hdUeflinta  is  almost  amorphous, 
consisting  only  of  the  ground-mass  of  the  massive  rocks.  The  beds 
and  mass-deposits  of  the  crystalline  rocks  are  often,  like  many  of  the 
Norwegian  deposits,  associated  with  talcose  and  chloritic  slates. 
Sometimes  limestone  is  also  present,  as  at  Falun,  Tunaberg,  etc., 
where  the  ores  lie  on  the  limestone  contacts.  The  ores  of  some  of 
the  deposits  suffer  in  depth  a  remarkable  change.  Thus  the  mass 
of  copper  pyrites  at  Falun  has  diminished  in  depth  ;  but,  on  the 
other  hand,  gold-bearing  quartz-  veins  appear  in  the  midst  of  the 
pyritic  body,  and  have  yielded  in  recent  years  considerable  amounts 
of  gold. 

Ammeberg.  —  I  will  cite  as  an  example  one  of  the  most  interesting 


*  "  Pragstufer  med  Braeciestruktur  fra   Muggruben   og   Stovarts,"  Magazin  for 
Naturvidens,  Kobern,  xxvii.,  B.,  p.  335. 


130  THE   GENESIS   OF   ORE-DEPOSITS. 

deposits,  namely,  the  zinc-blende  mine  of  Ammeberg,*  belonging  to 
the  Vieille  Montagne  Company,  which  I  have  personally  examined. 

In  a  winding  line,  chiefly  E.-W.,  and  about  3J  kilom.  (2  m.) 
in  length,  occur  steeply-dipping  beds  of  zinc  blende  in  gran u lite, 
or  gneiss  resembling  granulite.  At  certain  points  they  show  very 
beautiful,  close  folds.  At  first  glance  they  seem  to  be  genuine 
intercalated  beds  of  the  same  age  as  the  rock.  The  ores,  however, 
do  not  continue  along  the  whole  line,  but  form  separate  lenses, 
up  to  15  meters  (49  feet)  thick,  which  show  a  distinct  stratifi- 
cation, consisting  in  layers  of  fine-grained  to  amorphous  material 
resembling  halleflinta,  alternating  with  the  coarser  granulite.  Fig. 
96  is  a  polished  specimen,  which  exhibits  clearly  the  secondary 
ore-invasion.  The  original  bedding  is  here  indicated  by  a  series 
of  light  and  dark  dense  hallcflinta  layers;  and  these  are  broken 
through  by  masses  of  coarsely  crystalline  rock  and  of  ore.  The 
entrance  of  the  ore  into  the  coarsely  crystalline  layers  seems  to 
have  been  attended  by  an  enlargement  of  their  volume,  which  re- 
sulted in  their  breaking  through  the  dense  layers. 

The  same  explanation  is  required  for  some  parts  of  the  bed,  in 
which,  between  the  plane  surfaces  of  two  fine-grained,  barren  strata, 
ore  occurs  in  highly  folded  and  contorted  layers.  This  folding  is 
due  by  no  means  to  an  exterior  mechanical  energy,  but  to  interior 
chemical  forces 

Some  of  the  blende  layers  carry  a  considerable  admixture  of  ga- 
lena, as,  for  instance,  the  two  ore-layers  shown  in  Fig.  97,  separated 
by  a  fine-grained,  yellow  to  brown,  barren  stratum  of  eurite.  The 
whole  mass  is  traversed  by  fine  fissures  perpendicular  to  the  bedding, 
which  are  filled  with  leaf-silver,  looking  like  tin-foil.  A  replacement 
with  ore  of  the  original  rock-constituents  is  here  beyond  question. 

It  is  supposed  that  the  blende  has  taken  the  place  of  the  mica  of 
the  granulite.  But  the  whole  country-rock  also  is  metamorphous. 
At  the  open  cut  of  the  Godegard  II.  mine-working  I  found  in  the 
midst  of  the  schists  what  I  took  to  be  limestone,  but  I  subsequently 
lost  on  my  journey  the  specimens  intended  for  more  careful  examina- 
tion. But  petrographers  have  probably  long  since  determined  this 
point. 

This  Ammeberg,  deposit  then,  although  so  distinctly  bedded,  is 
by  no  means  of  primitive  origin ;  and  still  less  can  such  an  origin  be 
supposed  for  the  others,  which  occur  as  lenses  of  the  greatest  variety 

*  A  Sjogren,  "  Uridersokning  of  den  orogrifande  Bergarten  on  Ammebergs  Gruf- 
vor."  GeoL  Foreningens  i  Stockholm  Fb'rhandl.,  1880,  V. 


THE   GENESIS   OF   ORE-DEPOSITS.  131 

of  filling,  enclosed  in  the  crystalline  schists.  If  mica  may  be  replaced 
with  zinc-blende,  magnetite,  etc.,  such  a  change  will,  of  course,  be 
confined  to  certain  portions  of  the  rock,  immediately  within  range 
of  its  cause ;  and  these  portions,  as  distinguished  from  the  rest  of 
the  country-rock,  are  to  be  considered  mineral  deposits. 

Some  of  the  ore-deposits  of  the  Alps  have  a  certain  similarity  to 
those  of  Scandinavia,  for  instance,  Prettau,  in  the  Ahrn  valley,  in 
Tyrol;  Brennthal,  near  Miihlbach,  in  Salzburg;  and  Schneeberg, 
near  Sterzing,  in  Tyrol. 

Prettau  in  Tyrol. — There  is  here  a  very  ancient  copper-mining  in- 
dustry, which  was  overwhelmed  in  1878  by  a  great  disaster,  and  will 
not  soon  recover;  namely,  the  settlement  at  the  smelting-works  was 
buried  by  an  avalanche  so  deep  in  debris  that  it  has  been  necessary 
to  sink  shafts  nearly  20  meters  (65  feet)  deep  and  mine  out  the  stock 
of  manufactured  copper  and  other  objects  of  value. 

The  crystalline  schists,  which  here  strike  E.  and  W.,and  dip  steeply 
S.,  contain  impregnations  of  copper  and  iron  pyrites,  very  short  hori- 
zontally, but  considerably  prolonged  on  the  dip.  The  deposit  has 
been  opened  to  a  vertical  depth  of  500  meters  (1640  feet),  represent- 
ing 600  meters  (1968  feet),  so  that  the  horizontal  projection,  or  dis- 
tance between  the  top  and  bottom  is  only  350  meters  (1148  feet). 
Figs.  56  and  57  are  a  vertical  section  and  plan.  Figs.  54  and  55 
are  sketches  from  the  roof  and  side  of  the  Ottilie  gallery,  where  the 
chlorite-slate  and  pyrites  present  highly  complicated  forms,  some- 
what like  the  structure  I  have  observed  in  the  Transylvania  rock- 
salt.  It  may  be  explained,  in  my  opinion,  either  by  an  interior  in- 
crease of  volume  or  by  a  distortion  of  the  chlorite-slate  in  the  steep 
westward-pitching  line  indicated  by  the  ore-deposit.  It  is  extremely 
difficult  to  form  a  correct  conception  of  this  deposit.  I  was  able  to 
study  some  of  the  lower  levels  oniy. 

It  is  remarkable  that  the  pyrites- mine  of  Brennthal,  near  Miihl- 
bach, shows  an  entirely  similar  structure  and  form  of  ore-bodies,  and 
almost  the  same  westward  pitch  upon  the  E.— W.  plane  of  the  strati- 
fication. It  looks  as  if  dynamic  movements  connected  with  the 
mountain  had  played  a  leading  part  in  thus  determining  the  same 
pitch  for  the  ore-bodies  of  deposits  on  opposite  sides  of  the  Cen- 
tral Alps. 

Where  the  ore-body  begins  to  grow  poor,  and  the  pyrites  appear 
disseminated  in  grains  and  crystals  through  the  chlorite,  the  sec- 
ondary character  of  the  impregnation  is  clearly  recognizable.  The 
space  for  the  massive  ore-body  was  probably  prepared  by  mechanical 


132  THE   GENESIS   OF   ORE-DEPOSITS. 

forces.  That  a  metamorphosis  was  the  cause  is  not  likely,  because 
the  original  minerals  of  the  stratified  group  could  scarcely  have 
assumed  such  abnormal  form  and  dimensions. 

The  older  rocks  occupy  in  America  large  areas ;  and  there  also 
many  ore-deposits  occur  and  are  worked  which,  although  somewhat 
unlike  those  of  Scandinavia,  belong  to  a  similar  type.  I  do  not 
intend  to  describe  here  the  numerous  and  well-known  ore-deposits 
of  the  Eastern  and  Northern  States  ;  but  I  cannot  avoid  brief  men- 
tion of  some  peculiar  types. 

Lake  Superior. — The  copper-district  of  Lake  Superior  offers  a 
number  of  very  interesting  occurrences,  some  of  which,  though 
developed  by  extensive  mining,  and  often  described  at  considerable 
length,  have  not  yet  been  satisfactorily  explained.  It  is  remarkable 
that  copper  and  silver  occur  here  almost  exclusively  native;  but  it 
is  very  generally  admitted  that  this  is  not  the  usual  primitive  form 
of  copper.  Sulphides  seem  to  occur  but  seldom,  and  they  receive, 
as  a  rule,  no  attention.  I  saw  once,  at  Lac-la-Belle,  an  old  working 
upon  pyrite,  chalcosite  and  galena,  which  was  said  to  have  carried 
some  native  copper  in  its  upper  levels.  But  Foster  and  Whitney  do 
not  mention  it.* 

The  native  copper  of  this  district  occurs  notoriously  in  both  veins 
and  beds,  in  a  stratified  group  lying  between  the  Huronian  and  the 
Cambrian,  and  traversed  by  numerous  flows  of  eruptive  rocks.f  We 
are  here  concerned  with  the  beds.  The  ore  in  the  Calumet  and 
Hecla  mine  is  a  conglomerate  of  porphyry  pebbles  ;  another,  in  the 
Copper  Falls  mine,  is  a  dark  lava-flow,  the  so-called  "ash-bed." 
The  latter  is  impregnated  with  copper  on  both  sides  of  the  Owl 
Creek  vein,  which  traverses  it  (Fig.  98) ;  while  in  the  Calumet  and 
Hecla  conglomerate,  copper  sometimes  constitutes  the  cementing 
material. 

In  both  masses  the  spaces  now  filled  with  copper  were  unques- 
tionably once  filled  with  other  substances ;  and  the  present  condi- 
tions are  the  result  of  whole  series  of  complicated  replacements. 

R.  Pumpelly,  who  originally  believed  in  a  contemporaneous  ori- 

*  Report  on  the  Geology  and  Topography  of  a  Portion  of  the  Lake  Superior  Sand- 
District,  i.,  Washington,  1850,  p.  139. 

f  M.  E.  Wadsworth,  "  Notes  on  the  Geology  of  the  Inland  Copper-Dist.  of  L. 
Superior,"  Bvdl  of  Mus.  of  Comp.  Zool,  Harvard  College,  Cambridge,  vii.,  1880. 

E.  Pumpelly,  "  The  Paragenesis  and  Derivation  of  Copper  and  its  Associates  on 
Lake  Superior,"  Am.  Jour.  Sci.,  1872,  iii. 

R.  Duer  Irving,  "  The  Copper-bearing  Rock  of  L.  Superior,"  U.  S.  Geol.  Sur., 
3d  Ann.  Rep.,  Washington,  1883. 


THE   GENESIS   OF   ORE-DEPOSITS.  133 

gin  of  the  copper  and  the  enclosing  rock,  became  subsequently 
convinced  that  the  copper  had  replaced  especially  epidote  and 
chlorite,  and  that  certain  phases  of  metasomatic  processes  were  here 
represented.  The  eruptive  rocks  have  usually  been  strongly  at- 
tacked— for  instance,  the  pebbles  of  the  conglomerate,  the  rocks  on 
Isle  Royale,  etc.  Some  portions,  on  the  other  hand,  e.g.,  the  Ash- 
bed,  have  been  little  attacked.  The  former  instance  (which  the 
latter,  it  is  true,  contradicts)  was  used,  long  before  Sandberger,  as 
proof  of  a  sort  of  lateral-secretion  theory ;  and  now  and  then,  where 
the  copper-bearing  rock  was  overlain  by  an  eruptive  flow,  the  the- 
ory of  descending  solutions  was  also  brought  into  play. 

Some  of  the  attempted  explanations  assume,  in  my  opinion  cor- 
rectly, as  the  cause  of  the  first  ore-depositions,  the  action  of  hot 
springs — in  which  connection  it  is  only  to  be  emphasized  that  these 
thermal  effects  occurred  long  after  the  intrusion  of  the  eruptive 
flows  between  the  sedimentary  strata,  so  that  the  ores  were  brought, 
not  by  or  in  the  eruptives  themselves,  but  by  the  later  springs,  from 
great  depths  and  perhaps  from  considerable  distances.  This  ex- 
planation, applicable  to  all  the  deposits,  suits  also  the  exceptional 
case  cited  by  R.  I).  Irving,  namely,  the  Nonesuch  copper-bed  in  the 
sandstone  of  Porcupine  Mountain,  far  from  an  eruptive  outflow. 

As  to  the  condition  in  which  the  ores  were  first  deposited,  and  the 
manner  in  which  they  became  reduced  and  associated  with  zeolites, 
additional  data  must  be  sought  for  the  formation  of  an  opinion. 

Sudbury,  Canada. — Quite  recently,  A.  B.  von  Foullon  has  pub- 
lished his  observations  in  the  Sudbury  region,  Canada,*  expressing 
certain  theoretical  conclusions  of  great  interest,  which,  however, 
flatly  contradicted  my  view.  They  concern  the  pyritic  deposits  which 
occur  in  Huronian  rocks,  but  at  the  borders  of  eruptive  outflows  of 
diorite,  etc.,  and  were  described  by  T.  G.  Bonneyf  and  afterward  by 
R.  Bell.J  The  ores  are  associated  with  masses  of  diorite,  intercala- 
ted conformably  in  the  stratified  rocks.  The  ore-bodies  have  the  form 
of  "stock works/'  and  consist  of  an  irregular  mixture  of  rock  and 
metallic. sulphides  (?).  In  the  ore,  which  contains  gold,  platinum, 
tin,  lead,  silver,  zinc  and  iron,  occur  also  feldspar,  quartz  and  apatite. 
This  account,  taken  from  Bell's  description,  indicates  a  strong  anal- 
ogy with  the  Scandinavian  deposits. 

*  "Ueber  einige  Nickelerzvorkommen,"  Jahrb.  d.  k.  k.  E.  A.,  xliii.,  1892,  p.  276. 

f  "  Notes  on  a  Part  of  the  Huronian  Series  in  the  Neighborhood  of  Sudbury," 
Quart.  Jour.,  B.,  xliv.,  1888. 

I  "The  Nickel- and  Copper-Deposits  of  Sudbury  District,"  Bull.  Geol.  So&.  of 
Am.,  ii.,  Rochester,  1891. 


134  THE   GENESIS   OF   ORE-DEPOSITS. 

Foullon,  who  made  in  this  field  a  series  of  highly  valuable  obser- 
vations, supported  by  'careful  chemical  analyses,  expresses  himself 
finally  concerning  the  genesis  of  these  deposits,  as  follows  : 

"  The  irregular  mixture  of  pyrites  and  silicates,  presenting  copper  pyrites  and 
magnetic  pyrites  enclosed  in  the  rock  in  the  most  varied  quantities  and  in  all  con- 
ceivable forms;  and,  furthermore,  the  circumstance  that  sometimes  the  ore  occurs 
disseminated  in  the  diorite,  and  sometimes  the  diorite  is  enclosed  in  the  ore,  now 
the  rock,  and  again  the  pyrites,  being  the  ground-mass,  prove  unmistakably  their 
contemporaneous  origin.  At  certain  periods  of  the  diorite  eruption,  the  magma 
was  rich  in  accessory  constituents  which  rendered  possible  the  formation  of  the  me- 
tallic sulphides;  and  these  were  segregated  during  solidification." 

R.  Bell  has  expressed  himself  still  more  plainly. 

"  The  ores  are  not  of  humid,  but  of  molten  origin,  as  is  proved  by  their  occur- 
rence in  the  diorite.  with  which  they  ascended.  The  masses  of  molten  diorite  must 
have  remained  long  liquid,  so  that  the  metallic  sulphides  could  separate,  become 
concentrated  at  certain  points,  and  continue  with  the  fragments  of  diorite.  Large 
quantities  of  the  molten  diorite,  and  the  heavy  metals,  must  have  retired  again." 

These  surprising  statements  assume  a  chemical  impossibility, 
namely,  the  presence  of  metallic  sulphides  in  the  magma  of  the 
molten  eruptive  rock,  after  the  fashion  conceived  by  H.  C.  von 
Leonhard,*  on  the  strength  of  metallurgical  analogies. 

Shaft-furnaces,  operated  for  a  separation  of  the  ingredients  of  the 
charge,  produce  slag,  metallic  sulphides  (matte)  and  reguline  metal. 
But  the  above  hypothesis  involves  rather  a  common  fusion  of  all, 
and  a  separation  in  cooling  of  slag  (diorite)  and  matte  (metallic  sul- 
phides). These  authors  should  certainly  not  omit  to  explain  further 
the  principles  upon  which  their  explanation  is  based,  taking  into 
consideration  at  the  same  time  the  inner  structure  and  other  relations 
of  the  deposits  in  question,  such  as  their  conformity  with  the  strati- 
fied rocks  of  the  region  ;  the  occurrence  of  ore-channels,  quite  simi- 
lar to  those  encountered  in  deposits  formed  by  aqueous  circulation, 
etc. 

These  pyritic  deposits  contain  almost  all  the  heavy  metals,  inclu- 
ding platinum  and  gold,  and  it  is  remarkable  that  the  latter  here 
occurs  in  quartz,  exactly  as  it  does  generally,  throughout  the  world. 

The  untenable  character  of  the  explanations  above  quoted  must 
be  evident,  and  this  brief  mention  of  them  will  be  sufficient.  Yet 
it  appears  that  there  are  other  inquirers  into  the  genesis  of  ore-de- 
posits who  purpose  to  take  a  similar  standpoint.f 

*  Huttenerzeugnisse  und  andere  auf  kiinstlichem  Wege  gebildete  Mineralien  als  Stutz- 
punkte  geologischer  Hypothesen,  Stuttgart,  1858. 

f  For  instance,  J.  H.  L.  Vogt,  of  Christiania,  "Bildung  von  Erzlagerstiitten 


THE   GENESIS   OP   ORE-DEPOSITS.  135 

4.  HYSTEROMORPHOUS  DEPOSITS. 

Under  this  title  are  included  the  deposits  formed  by  the  chemical 
and  mechanical  influences  of  the  surface- region,  from  the  original 
deposits  of  which  the  conditions  of  origin  have  been  considered 
above.  These  formations  have  been  considered  and  named  from 
various  standpoints.  Thus  the  name  "deposits  of  debris"  empha- 
sizes the  idea  of  a  mechanical  crushing  or  disintegration  ;  the  Ger- 
man term  Seife,  like  the  Spanish  and  American  "  placer,"  is  based 
upon  the  manner  in  which  such  deposits  are  often  mined  for  their 
metallic  contents,  and  so  on.  The  expression  "secondary  deposits" 
satisfies,  it  is  true,  the  definition  given  above,  but  is  rendered  am- 
biguous by  its  frequent  use  in  other  meanings  connected  with  the 
genesis  of  ores.  I  feel  warranted,  therefore,  in  proposing  for  this 
group  the  more  distinctly  significant  name  "  hysteromorphous " 
(later-formed). 

The  influences  of  the  present  surface  upon  deposits  found  in  the 
deep  region  are  so  characteristic  as  to  permit  us  to  draw  conclusions 
concerning  the  processes  of  earlier  periods,  when  the  surface  occupied 
a  very  different  position.  Unquestionably,  effects  similar  to  those  of 
to-day  were  produced  then  also,  and  we  must  include  in  our  con- 
sideration of  the  subject  the  hysteromorphism  of  former  geological 
periods.  • 

a.   Chemical  Effects. 

The  chemical  effects  proceeding  from  the  present  surface  have 
been  already  discussed  in  many  respects.  They  involve  not  only 
phenomena  on  the  surface  itself,  but  extend  beneath  it  to  the  ground- 
water  level,  and  even  below  that  level,  so  far  as  the  vadose  circula- 
tion is  traceable. 

On  the  surface  it  is  especially  the  oxidizing  effect  of  the  atmos- 
phere, its  contained  carbonic  acid,  and  the  solvent  and  chloridizing 
action  of  atmospheric  precipitation,  simultaneously  aided  by  the  me- 
chanical effects  of  wind  and  moving  water,  which  bring  about  what 
Justus  Roth*  has  called  "  simple  weathering,"  to  distinguish  it  from 
more  complicated  forms  of  decomposition.  In  considering  not 
merely  rocks,  but  outcrops  of  complex  ore-deposits,  we  encounter 
what  Roth  calls  "  complicated  weathering." 

Decomposition    underground,    through   the   action    of  the   same 

durch  Differentiationsprozesse  im   basischen  Eruptionsmagma." — Zeitsch.f.  prakt. 
Gaol,  1893,  i.,  p.  4. 
*  Allgem.  u.  Chem.  Geologic,  vol.  i.,  Berlin,  1879,  pp.  69-159. 


136  THE   GENESIS   OF   ORE-DEPOSITS. 

atmospheric  constituents  of  the  surface-water,  extends,  as  is  well- 
known,  to  the  ground-water  level,  where  it  may  manifest  itself 
in  a  striking  way  by  reason  of  the  frequent  occurrence  at  that  level 
of  the  alternation  of  dry  ness  with  moisture,  which  is  a  factor  greatly 
promoting  decomposition. 

A  similar  condition  is  presented,  as  was  pointed  out  in  Part  I., 
by  the  workings  of  mines,  where  the  water-level  has  been  artificially 
lowered,  and  a  zone  of  depth  previously  untouched  by  the  vaclose 
circulation  is  brought  within  the  domain  of  that  agency.  Deep  and 
old  metal-mines  especially  exhibit  in  a  striking  way  the  effects  of 
the  vadose  circulation,  and,  in  addition,  a  phenomenon  but  seldom 
found  in  places  under  the  influence  of  the  natural  water-level, 
namely,  the  effect  of  the  mine-waters  upon  various  surface  relations 
and  products. 

Limonite-Deposit  near  Rio  Tinto,  Spain. — One  of  these  rare  in- 
stances is  cited  by  J.  A.  Phillips*  in  his  group,  "Deposits  resulting 
from  chemical  action."  Namely,  in  the  vicinity  of  the  great  iron 
and  copper  pyrites-deposits  of  Rio  Tinto,  in  Spain,  there  occurs  a 
deposit  of  hydrated  ferric  oxide,  shown  by  the  fossils  it  contains 
(which  correspond  with  species  still  living  in  the  region)  to  be  of 
recent  origin,  and  undoubtedly  produced  by  the  weathering  and  de- 
composition of  the  neighboripg  pyritic  deposit.  It  was  deposited 
in  a  swamp-like  basin  with  peaty  matter,  and  subsequent  erosion  has 
left  of  it  two  remnants  only,  at  Mesa  de  los  Pinos  and  Cerro  de  las 
Vacas  respectively.  Evidently,  in  this  case,  the  detritus  of  the  py- 
ritic deposit  has  not  been  mechanically  swept  away  and  collected 
elsewhere,  but  a  chemical  action  has  taken  place,  removing  material 
in  solution,  exactly  as  in  the  formation  of  bog  iron-ores.  The 
formation  here  is  certainly  earlier  than  the  Roman  period,  for  Roman 
tombstones  have  been  found,  made  of  this  recent  iron-ore. 

Mine- waters  contain  the  solutions  of  all  substances  directly  or  in- 
directly dissolved  by  the  vadose  circulation,  and  some  of  these,  en- 
countering suitable  precipitants,  may  be  thrown  down.  Thus,  ferrous 
oxide  becomes  by  oxidation  hydrated  ferric  oxide;  many  metallic 
sulphates  are  reduced  by  organic  matter  to  sulphides ;  copper-salts 
may  even  be  thus  reduced  to  metal,  etc.  These  new  precipitates  will 
mark  the  track  of  the  mine- waters. 

Finally,  while  the  solutions  formed  by  surface-waters,  like  those 
of  the  mine-waters,  mostly  find  their  way  to  the  points  where  the 

*  A  Treatise  on  Ore-Deposits,  London,  1884,  p.  15. 


THE  GENESIS   OF  ORE-DEPOSITS.  137 

water-level  reaches  the  surface  (drainage-points),  yet  as  a  part  of  the 
ground- water  penetrates  to  greater  depths,  such  solutions  may  very 
likely  produce,  in  the  deep  region  itself,  impregnations,  which  must, 
ho\\ever,  differ  in  character  from  those  produced  by  the  deep  circula- 
tion proper. 

The  primitive  deposit  from  which  such  solutions  have  come  will 
show  remaining  in  it  principally  substances  not  easily  soluble,  to- 
gether with  such  as,  like  precious  stones,  resist  all  atmospheric  influ- 
ences. Meteoric  waters,  carrying  oxygen,  some  carbonic  acid,  and 
small  quantities  of  chlorides,  will  first  oxidize  whatever  is  oxidiza- 
ble,  especially  the  metallic  sulphides.  On  this  subject  S.  H.  Em- 
mens*  has  published  a  clear  statement,  with  some  practical  deduc- 
tions. He  distinguishes  in  the  order  of  liability  to  decomposition 
the  following  degrees:  (1)  marcasite,  (2)  pyrite,  (3)  pyrrhotite,  (4) 
chalcopyrite,  (5)  bornite,  (6)  folgerite,  (7)  millerite,  (8)  chalcosite, 
(9)  galena,  and  (10)  zinc-blende.  The  acid  ferric  sulphate  formed 
from  the  first  members  of  this  series  immediately  attacks  the  latter 
members.  The  carbonic  acid  contained  in  the  circulating  waters  has 
a  high  solvent  power,  and,  among  other  things,  dissolves  the  carbo- 
nate of  lime  as  a  bicarbonate,  which  reacts  upon  the  basic  sulphates, 
producing  gypsum  and  free  carbonic  acid,  and  ultimately  transform- 
ing lead  sulphate  into  carbonate  (cerussite).  Copper  oxide  and, 
under  some  circumstances,  native  copper,  may  be  formed  from  copper 
sulphate,  and- so  on. 

For  the  chlorine  of  the  chlorides,  lead  and  silver  have  the  strongest 
affinity,  and  these  metals  will  consequently  be  often  found  in  the 
upper  zone  as  chlorides. 

The  decomposition  above  water-level  of  gold-  and  silver-bearing 
deposits  facilitates  the  extraction  of  these  metals.  Metallic  gold  can 
be  extracted  by  simple  processes  of  mechanical  concentration  and 
amalgamation  from  oxidized  material,  while  gold  in  undecomposed 
sulphides,  etc.,  must  be  roasted,  smelted,  or  chlorinated  with  more 
or  less  cost  and  difficulty.  Silver  likewise  occurs,  as  a  rule,  in  this 
upper  decomposed  zone  in  the  form  of  easily  amalgamated  combina- 
tions (free-milling  ores),  while  the  refractory  ores  of  deeper  zones  are 
much  harder  to  treat. 

It  is  doubtless  for  these  reasons  that  mining  enterprises  often  come 
into  very  critical  conditions  when  they  reach  water  level,  and  many 
mines  even  cease  to  be  profitable.  An  important  part,  no  doubt,  is 

*  "  The  Chemistry  of  Gossan,"  E.  and  M.  J.,  1892,  liv.,  p.  582. 


138  THE   GENESIS   OF   ORE-DEPOSITS. 

played  by  other  causes,  such  as  the  necessity  of  hoisting  increased 
quantities  of  'water,  the  cost  of  the  required  machinery,  etc. 

It  is  remarkable  that  irt  western  North  America  the  ground-water 
level  lies  deeper  than  is  generally  the  case  in  Europe.  I  suppose 
the  reason  to  be,  that  the  present  area  of  the  Interior  Basin  of  North 
America,  which  has  no  surface-drainage  to  the  ocean,  was  formerly 
cut  by  deep  valleys  of  erosion,  which  made  a  deeper  escape  of  the 
ground-water  possible.  This  suggestion  is  confirmed  by  the  level 
valleys  of  Utah  and  Nevada,  several  miles  wide  and  filled  with  very 
recent  sediments,  between  comparatively  narrow  mountain  ranges, 
which  seem  to  be,  so  to  speak,  the  tops  only  of  the  former  ranges. 

In  Europe,  the  upper  zones  of  the  ore-deposits  were  worked  out 
long  ago,  at  a  time  when  the  science  of  chemistry  was  in  its  infancy. 
But  we  know  from  the  remnants  in  these  workings  that  chlorides, 
lead  and  silver  carbonates,  and  various  sulphates,  such  as  anglesite, 
occurred  in  them,  though  they  were  not  recognized.  In  Transylvania 
the  decomposed  products  of  the  outcrop-zone  were  called  Braunen 
("  browns"),  with  evident  reference  to  the  brown  hydrated  ferric 
oxide.  The  well-known  maxim  of  the  German  miners  concerning 
the  "  iron  hat "  is  very  ancient ;  and  the  same  may  be  said  of  the 
Cornish  proverb,  "  Gossan  rides  a  high  horse."  Litnonite  is  cer- 
tainly a  characteristic  indication  of  the  outcrop  of  an  ore-deposit ; 
and  no  doubt  its  reddish-brown  color  has  chiefly  suggested  the 
South  American  miners'  names,  pacos  and  colorados. 

In  a  few  instances  the  te  iron  hat"  has  been  actually  mined  as  an 
iron  ore.  As  a  rule,  it  is  the  decomposed,  porous  and  honey-combed 
vein-material  of  the  upper  zone,  and  is  colored  only  with  limonite. 
The  part  of  the  ore-deposit  above  water-level  has  a  characteristic 
appearance.  Quartz  and  other  refractory  gangue-minerals  are  sur- 
rounded and  impregnated  by  earthy  liraonite  masses.  As  a  rule  the 
original  texture  of  the  deposit  has  become  obscure;  and  sometimes 
fragments  of  the  mineral  crusts,  broken  off  and  crushed  through 
changes  of  voluiie,  are  found  chaotically  thrown  together.  Occa- 
sionally, however,  the  original  structure  may  still  be  traced  in  the 
decomposition-products  of  the  several  crusts,  unaltered  nuclei  of  the 
ore  being  discoverable  in  them.  Some  substances  (especially  cala- 
mine  formed  from  zincblende)  display  the  stalactitic  forms  char- 
acteristic of  the  vadose  region.  Original  druses  as  well  as  recently 
formed  cavities  are  filled  with  new  material ;  and  in  this  way  a 
secondary  crust ification  may  occur. 

I  must  not  forget  to  mention   that  there  are  some  observations 


THE   GENESIS   OF   ORE-DEPOSITS.  139 

according  to  which  gold  has  been  precipitated  chemically  in  hystero- 
morphous  deposits.  Oscar  Lieber,*  F.  A.  Genth  and  A.  R.  C.  Selwyn 
expressed  the  opinion  that  detrital  gold  generally,  or  a  portion  of  it, 
has  been  deposited  from  solutions.  Laur,  J.  A.  Phillips,  Wilkin- 
son, Newberry,  Daintree,**  Skey,  Egleston,f  etc.,  have  accepted  this 
view  as  more  or  less  generally  applicable.  E.  CohenJ  has  undertaken 
to  examine  it  critically,  and  is  inclined  by  his  own  experience  in 
South  Africa  "  to  adopt  the  conclusion  reached  by  Devereux  for  the 
Black  Hills  of  Dakota,  and  to  assume  that  by  far  the  largest  part 
of  the  detrital  gold  has  been  liberated  by  the  mechanical  destruction 
of  older  deposits  and  has  been  mechanically  laid  down  ;  while,  on 
the  other  hand,  a  precipitation  from  solutions  undoubtedly  takes 
place,  but  plays  a  very  subordinate  part  only." 

My  own  opinion  on  the  subject  is  expressed  in  the  above  quotation. § 
No  doubt  here  and  there,  in  the  detrital  deposits,  traces  of  chemical 
activity  are  discoverable;  but  they  are  not  sufficient  to  weaken  the 
evident  proofs  of  the  mechanical  origin  of  detrital  gold. 

b.  Mechanical  Effects. 

The  mechanical  effects  of  moving  air  and  water,  of  frost  and  ice, 
are  grouped  under  the  head  of  erosion,  and  are  treated  at  length,  so 
far  as  rocks  in  general  are  concerned,  in  the  geological  text-books. 
We  are  here  concerned  especially  with  effects  of  this  kind  produced 
upon  those  portions  of  ore-deposits  which  are  exposed  at  the  surface. 
We  notice  at  once  that  mechanical,  unlike  chemical  effects,  are  con- 
fined to  the  surface  or  a  very  small  distance  below  it.  In  general, 
we  must  assume  that  the  chemical  changes  took  place  first,  but  that 
the  progress  of  erosion  brings  both  to  our  view  at  the  same  time. 

Verchoviky,  or  Surf  ace- Deposits  in  Situ. — Not  only  water  and  ice 
(glaciers),  but  also  wind,  takes  part  in  erosion.  For  instance,  if  an 
ore-deposit,  by  reason  of  its  greater  resistance,  crops  out  above  the 
level  of  the  country,  the  wind  will  continually  tend  to  blow  away 
the  finer  and  lighter  portions  of  the  detrites  formed  by  chemical 


*  In  Cotta's  Gangstudien,  and  in  Geol  Rep.  of  8.  Carolina,  1860. 

**  See  A.  G.  Lock's    Gold,  its  Occurrence  and  Extraction,  p.  746-800. 

f  "  The  Formation  of  Gold  Nuggets  and  Placer-Deposits,"  Trans.  A.  I.  M.  E., 
ix.,  1881,  p.  633. 

J  "Ueberdie  Entstehung  des  Seifengoldes,"  Mitth.  d.  Naturw.  Vereinsf.  Neypom- 
mern  u.  Rilgen,  xix.,  1887. 

$  See  my  article,  "  Zur  Genesis  der  Metallseifen,"  Oesterr.  Zeitsch.f.  B.  u.  H.  wesen, 
1887,  xxxv.,  p.  325. 


140  THE   GENESIS   OF   ORE-DEPOSITS. 

processes  of  weathering;  so  that,  in  the  course  of  time,  there  must 
remain  of  the  original  outcrop  only  the  heavier  portions,  so  far  as 
these  are  not  carried  away  by  water.  In  fact,  I  have  observed  in 
the  Urals  that  the  gold-diggings  of  the  valley,  undoubtedly  formed 
by  water,  extended  up  the  slopes  to  points  where  this  could  not 
have  been  their  origin.  The  gold-bearing  weathering-detritus  is 
then  called  Nagornyje  rozsypy  and  Verchoviky. 

A  similar  feature  was  observed  by  W.  C.  Kerr*  in  the  auriferous 
deposits  of  North  Carolina ;  and  I  have  seen  it  in  the  old  gold- 
workings  of  Bergreichenstein  and  Nesvacil,  in  Bohemia,f  where  flat 
mountain  ridges  are  covered  with  old  pits  and  dumps.  It  is  im- 
possible to  consider  them  as  diluvial  terraces,  for  the  alluvium 
passes  over,  so  to  say,  into  the  solid  gneissic  rock,  which  is  traversed 
by  many  quartz  veins.  The  gold  occurs  concentrated  in  the  deepest 
portion  of  the  weather-detritus,  that  is  to  say  on  the  contact  with 
bed-rock,  and  has  penetrated  all  the  open,  loosely-filled  fissures  in 
the  latter. 

CottaJ  speaks  also  of  deposits  of  debris  in  place,  which  occur 
on  high  plateaus  and  mountain  slopes,  and  consist  of  products  of 
weathering  which  are  not  rounded  pebbles  or  sand  and  slime,  accu- 
mulated by  water-currents.  A.  G.  Lock§  speaks  of  surface-deposits 
being  "a  result  of  the  disintegration  of  the  rocks  in  situ"  and  says  : 

"  The  gold  it  contains  is  quite  angular,  hackly,  or  crystalline,  and  is  derived 
fromauriferous  quartz  reefs  or  leaders,  existing  in  the  immediate  vicinity." 

Similar  conditions  obtain  very  significantly  in  the  Kaekar  dis- 
trict, to  be  hereinafter  more  fully  described. 

Ttieory  of  the  Sinking  of  Heavier  Constituents. — But  the  great 
agent  in  the  transportation  and  re-deposition  of  the  metallic  por- 
tions of  original  deposits  has  unquestionably  been  flowing  water ; 
and  this  is  an  equal  factor  in  the  removal  of  the  rock-detritus  of 
erosion,  which  it  is  constantly  striving  to  carry  to  the  ocean. 
River-sediments  are  notoriously  unstable.  What  is  deposited  this 
year  is  carried  further  down  stream  in  the  years  next  following, 
and  so  on  until  it  comes  to  comparative  rest  in  the  sea.  The 

*  "  Some  Peculiarities  in  the  Occurrence  of  Gold  in  North  Carolina,"  Trans.  A. 
I.  M.  R,  x.,  475. 

f  "Zur  Genesis  der  Metallseifen,"  Oeslerr.  Z.  f.  B.  u.  H.  wesen,  1887,  xxxv., 
p.  325. 

t  Erzlagerstatien,  i.,  Freiberg,  1859,  p.  100. 

g  Gold,  its  Occurrence,  etc.,  London,  1882,  p.  828. 


THE   GENESIS   OF   ORE-DEPOSITS.  141 

original  deposits,  furnishing  the  material  thus  transported  over 
great  distances  and  areas  by  water,  are  well  called  by  the  Russians 
Korennyje  mestorozdenyje,  or  root-like  deposits, — that  is,  as  it  were, 
the  roots  of  the  scattered  hysteromorphous  deposits. 

The  attempt  has  been  made  to  explain  the  concentration,  especially 
of  heavy  metals,  like  gold  and  platinum,  in  certain  paying  layers  of 
the  detritus,  by  a  sort  of  natural  concentration  process.  The  cir- 
cumstance that  the  richest  gold-deposits  most  frequently  lie  in  the 
lowest  stratum  of  the  detritus,  immediately  on  the  bed-rock,  yet 
that  several  such  horizons  occur  one  over  the  other,  is  difficult  to 
explain  in  this  way;  for  Cotta's  assumed  separate  periods  of  forma- 
tion (op.  cit.  i.  p.  102)  are  scarcely  satisfactory,  involving  as  they  do 
either  periodic  transportation  or  periodic  deposition,  neither  of  which 
is  probable. 

I  believe  that  I  have  found  in  the  Ural  gold-placers  a  much  more 
probable  explanation,  based  on  the  principle  that  the  specifically 
heavier  elements  of  a  loose  mass  are  able,  with  the  aid  of  water,  to 
work  their  way  down  through  the  lighter  portions.  At  the  Przibram 
concentrating- works,  it  is  found  that  if  the  pulp  is  left  standing  for 
a  considerable  period,  the  galena  will  accumulate  at  the  bottom.  In 
gold- and  platinum-concentrating  establishments,  it  may  be  often 
observed  that  these  heavy  metals  find  their  way  into  the  floor  and 
woodwork  of  the  mill,  from  out  of  which  they  are  from  time  to  time 
recovered  by  working  up  these  materials.  Why  should  this  happen 
in  artificial  operations  only,  and  not  also  under  natural  conditions, 
where  the  descent  of  the  heavier  portions  is  essentially  aided  by  the 
percolation  of  atmospheric  waters  through  the  loose  covering-mater- 
ial? 

This  view  is  supported  by  the  features  of  all  gold-placers,  espec- 
ially those  of  the  detritus  of  weathering  in  place,  where  the  agency 
of  running  water  cannot  be  adduced,  and  the  accumulations  of  gold 
at  the  contact  of  the  loose  and  the  solid  material  must  be  explained 
by  its  sinking  through  the  former. 

Sir  earn- Detritus. — The  detrital  deposits  produced  by  running 
water  are  generally  characterized  by  the  predominance  of  permeable 
material,  such  as  sand,  gravel,  etc.  Under  this  covering  mass  lies 
the  solid,  impermeable  "  bed-rock  "  or  "  rim-rock  "  of  the  Americans, 
the  plotik  or  posva  of  the  Russians ;  and  in  all  the  gold-fields  of  the 
world,  the  richest  pay -deposits  are  found,  as  a  rule,  at  the  border 
between  the  cover  and  the  bed-rock.  If  the  latter  is  decomposed, 
fissured,  or  otherwise  loosened,  the  fine  gold  will  sink  into  it,  mak- 


142  THE   GENESIS   OF   ORE-DEPOSITS. 

ing  it  sometimes  rich  enough  to  be  mined  and  concentrated ;  and 
this  occurs  without  regard  to  the  petrographic  character  of  the  rock. 
Thus  in  the  Ural,  palaeozoic  schists,  limestone  and  eruptive  rocks 
indifferently  are  charged  with  gold.  This  circumstance  indicates 
also  the  error  of  the  assumption  that  these  bed-rocks  originally  car- 
ried gold. 

But  layers  of  impermeable  material  sometimes  occur  in  the  cover, 
as,  for  instance,  lava-beds  in  Australia  and  California,  or,  in  general, 
solid  conglomerates  and  clays.  In  such  cases  there  is  often  a  con- 
centration of  gold  on  the  more  solid  layer,  called  in  America  the 
"  false  bottom,"  and  in  the  Ural  loznyj  plotik — that  is,  a  material 
erroneously  taken  for  the  bed-rock.  There  are  often  in  the  detrital 
cover  two  or  more  such  gold-bearing  layers,  which  are  easily  ex- 
plained on  the  theory  above  suggested.  The  hypothesis  of  a  natural 
concentration  in  running  water  is  embarrassed  by  the  fact  that  the 
material  of  gold-placers  shows  no  arrangement  according  to  size, 
but  consists,  as  a  rule,  of  elements  of  all  sizes. 

The  movement  of  the  elements  of  a  loose  mass  has  been  already 
pointed  out  by  W.  C.  Kerr,*  who  admits  the  possibility,  according 
to  A.  G.  Lock,  of  the  sinking,  of  the  heavier  particles,  though  this 
is  only  in  a  passing  remark,  and  without  indication  of  its  far-reach- 
ing importance.  He  says : 

"The  superior  weight  of  the  precious  atoms  would  cause  them  to  sink  through 
the  moist  surrounding  matters,  till  a  hard  layer  was  met  with.  The  occurrence  of 
this  process  would  constantly  add  to  the  deposits,  the  gold  always  gravitating  to  the 
bottom,  quickly  or  slowly,  according  to  circumstances." 

It  seems  to  me  that  this  idea  must  have  impressed  itself  upon 
other  impartial  observers  also;  and  I  can  only  wonder  that  it  has 
not  been  more  frequently  expressed. 

R.  Helmhacker  has  recently  communicated  some  observations  in 
the  Altai  region  of  Siberia,  such  as  the  sinking  of  heavy  metallic 
objects  in  the  loose  wash,  which  confirm  the  above  views.  Among 
other  things,  he  identified  grains  of  metallic  lead  formed  in  the  gold- 
placers,  as  shot,  scattered  in  hunting,  which  had  sunk  into  the  earth. 

As  is  well  known,  auriferous  detritus  occurs  not  only  in  present 
but  also  in  ancient  river-beds,  long  since  dry;  and  since,  in  the 
latter,  the  remains  of  diluvial  animals,  such  as  the  mammoth,  etc., 
have  been  found,  a  distinction  has  been  made  between  alluvial  and 

*  "The  Gold-Gravels  of  North  Carolina,"  Trans.  A.  L  M.  R,  1880,  viii.,p.462. 
Gold,  its  occurrence,  etc.,  London,  1882,  p.  916. 


THE    GENESIS    OF    ORE-DEPOSITS.  143 

diluvial  gold-deposits.  But  discoveries  of  yet  older  organic  remains 
have  shown  that  such  gold-deposits  were  formed  in  still  more  ancient 
periods.  The  old  river-beds  of  California  cross  the  present  streams, 
and  the  auriferous  detritus  of  the  former  is  covered  with  thick  lava- 
beds — a  feature  which  may  be  observed  in  Australia  also.  During 
the  deposition  of  the  gold,  therefore,  conditions  very  different  from 
those  of  the  present  day  must  have  obtained. 

In  another  respect,  also,  the  relation  between  ancient  and  modern 
river-beds  is  sometimes  peculiar.  The  late  channels  have  been  ren- 
dered by  erosion  deeper  than  the  older  ones.  But  on  the  eastern  slope 
of  the  Ural  this  is  almost  totally  reversed.  The  diluvial  gold-deposits 
characterized  by  the  remains  of  the  mammoth  often  lie  below  the 
water-level  of  the  present  streams,  so  that  the  latter  must  be  diverted 
in  order  to  mine  the  ancient  beds.  This  condition  apparently  ex- 
tends throughout  the  whole  Siberian  plain,  and  may  be  taken  as 
evidence  that  the  erosive  energy  of  its  rivers  has  decreased  since  the 
Diluvial  period,  their  fall  having  been  reduced,  either  by  the  accu- 
mulation of  the  erosion-detritus  or  by  changes  in  the  relative  alti- 
tude of  the  Ural  range. 

The  eastern  slope  of  the  Ural  is  characterized  by  numerous  lakes 
and  swamps  along  the  tributary  streams,  and  a  number  of  these 
contain  auriferous  detritus,  which  has  been  mined  for  gold. 

Marine  Detritus. — In  some  regions,  the  auriferous  detritus,  after 
being  repeatedly  deposited  and  again  swept  away,  to  be  re-deposited 
further  down  the  valleys,  has  at  last  reached  the  sea.  The  coast  of 
Oregon,  in  western  North  America,  and  Vladivostock,  in  southeast- 
ern Siberia,  are  examples.  Here  the  ebb  and  flow  of  the  tide 
operate  very  nearly  on  the  principles  of  artificial  ore-dressing;  and 
one  would  think  that  a  concentration  of  the  heavier  particles  might 
be  thus  effected.  But  it  does  not  appear  that  such  effects  have  been 
recognized  hitherto. 

Kackar  District,  in  the  Ural. — At  the  beginning  of  this  section, 
in  the  discussion  of  features  of  auriferous  erosion  detritus,  some 
characteristics  of  the  Ural  placers  were  described.  A  few  additional 
particulars  concerning  them  may  be  of  interest.  The  gold-bearing 
stratum  occurs  at  no  definite  depth.  As  a  rule,  the  whole  of  the 
barren  or  poor  cover  is  stripped  off  and  thrown  aside,  before  the 
auriferous  layer,  thus  laid  bare,  is  systematically  attacked.  Open 
cuts  (Razregy)  in  the  surface,  of  greater  or  less  depth,  are  thus 
created,  and  are  usually  left  to  be  filled  up  by  the  rivers.  In  the 
district  of  Kackar,  already  mentioned,  in  the  Southern  Ural,  orig- 


144  THE   GENESIS   OF   ORE-DEPOSITS. 

inal  gold-deposits  (  "  root-deposits  "  )  of  gold  have  been  repeatedly 
found  in  the  bottom  of  these  cuts.  They  were  well-defined  quartz- 
veins,  carrying  in  the  upper  zone  free  gold,  but  at  greater  depth 
sulphides  and  arsenides  rich  in  gold.  In  the  case  I  have  in  mind, 
the  original  open  cut  extended  for  a  considerable  distance  along  the 
strike  of  the  vein  ;  but  the  bed-rock  (which  was  at  the  same  time 
the  country- rock  of  the  vein)  was  much  decomposed,  so  that  the 
difference  between  detritus  and  bed-rock  was  not  strikingly  evident ; 
and  the  placer- working  passed  only  by  gradual  stages  into  vein- 
mining. 

Hysteromorphous  gold-deposits  may  thus  be  said,  in  a  general 
way,  to  occur  in  the  following  positions  : 

1.  In  the  simple  detritus  of  weathering,  immediately  upon  the 
original  deposit  (  root-deposit ). 

2.  Mixed  with  the  sand  and  gravel  of  present  streams. 

3.  At  certain  points,  in  the   river-bottom,   into  the  crevices  and 
fissures  of  which  the  gold  has  sunk. 

4.  Mixed  with  the  impermeable  material  of  older  water- courses, 
through  which  the  gold  could  not  sink. 

5.  On  the  false  bottoms  or  bed-rocks. 
G.  On  the  true  bed-rock. 

7.  In  the  decomposed  bed-rock  itself. 

In  considering  the  chemical  changes  of  the  outcrops  of  deposits 
(including,  of  course,  those  which  give  rise  to  hysteromorphous 
derivatives)  we  have  seen  that  sulphides  suffer  total  decomposition, 
and  that  of  their  constituents  only  the  unoxidizable  metals,  such  as 
gold  and  platinum,  remain  unaffected.  Silver-ores  and  native 
silver,  being  attacked  by  the  chlorides  of  the  vadose  circulation,  are 
consequently  not  found  in  hysteromophous  deposits.  But  gold 
occurring  in  nature  is  for  the  most  part  alloyed  with  silver.  The 
gold  from  the  veins  of  Budweis,  in  Bohemia,  contains  by  weight 
about  two  parts  of  silver,  and  that  of  Transylvania  contains  by 
weight  more  than  three  of  silver,  to  ten  of  gold.  Whenever  I  have 
had  opportunity  to  compare  the  gold  of  an  original  or  root-deposit 
with  that  of  its  derived  placer,  I  have  found  the  latter  to  be  of 
greater  fineness,  that  is,  to  contain  less  silver.  I  am  strongly 
inclined  to  ascribe  this  phenomenon  to  the  prolonged  contact  with 
water  containing  chlorides.  The  dull  surface  of  placer-gold  and  its 
frequently  spongy  interior  structure,  as  compared  with  the  luster 
and  solidity  of  "  quartz-gold,"  favor  this  explanation. 

Platinum- Placer s. — Detrital  deposits  of  platinum  have  been,  until 


THE   GENESIS   OF   ORE-DEPOSITS.  145 

recently,  particularly  observed  in  the  Ural  only,  from  which  the 
main  supply  of  platinum  was  derived.  Additional  localities  are  now 
reported  in  the  Altai  district  of  Siberia  and  in  Canada  and  British 
Columbia.  In  the  Tulameen  district,  it  is  said,  the  hydraulic 
method  of  mining  has  been  introduced  for  platinum.  I  have  been 
unable  to  obtain  detailed  information  concerning  the  features  of 
these  deposits. 

In  the  Ural,  and  particularly  in  its  most  productive  district,  that 
of  Niznyj  Tagil,  the  conditions  closely  resemble  those  of  gold-de- 
posits. The  richest  platiniferous  layers  are  on  the  true  bed-rock. 
Platinum  and  its  associates,  palladium,  nevjanskite  and  siserskite, 
being  found  to  occur  occasionally  adhering  to  olivine  and  chromite, 
it  was  inferred  that  they  were  derived  from  the  serpentine,  which  is 
itself  a  secondary  product  from  olivine-rocks.  More  recently,  plati- 
num is  said  to  have  been  found  in  an  olivine-gabbro  not  yet  meta- 
morphosed ;  but  whether  the  metal  is  a  primary  or  an  exotic  con- 
stituent, can  as  yet  scarcely  be  declared  with  certainty. 

Formerly  no  other  occurrence  of  platinum  than  the  native  metal 
was  known;  but  now  a  platinum-ore  has  been  found  in  the  Sud- 
bury  district,  Canada,  namely,  sperrylite,  a  compound  of  platinum 
and  arsenic.  Since  this  is  certainly  xenogenous,  the  question  as  to 
the  original  sources  of  platinum -deposits  is  advanced  to  a  new  phase 
by  its  discovery. 

Tin-Placers. — In  connection  with  the  occurrence  of  tin  as  cassite- 
rite  in  detrital  deposits,  the  specific  gravity  (6.97)  of  this  mineral, 
nearly  equalling  that  of  iron,  and  the  great  resistance  which  it  offers 
to  natural  agents  of  decomposition,  doubtless  play  the  principal  part. 
Of  the  numerous  and  various  associates  of  cassiterite  in  its  original 
deposits,  none,  except  quartz,  are  equally  able  to  resist  decomposi- 
tion ;  and  the  consequence  is,  that  the  detritus,  both  of  weathering 
and  of  erosion,  from  the  outcrops  of  such  deposits,  contains,  besides 
the  products  of  the  decomposition  of  these  other  minerals,  chiefly 
quartz  and  pieces  of  cassiterite.  The  latter,  by  reason  of  its  high 
specific  gravity,  will  tend  to  sink  through  the  lighter  detritus  and 
be  concentrated  near  the  bed-rock. 

The  stanniferous  detrital  deposits  of  Bohemia  and  Saxony,  as  well 
as  Cornwall,  were  long  since  exhausted  ;  those  of  Australasia,  the 
South  Sea  islands  and  South  America  are  still  worked.  According 
to  the  special  monograph  of  Dr.  E.  Eeyer*,  the  richest  layers  are  in 

*  Zinn,  eine  geoL-montan.-historische  Monographic,  Berlin,  1881,  p.  208. 

10 


146  THE   GENESIS    OF   ORE-DEPOSITS. 

fact  found  at  the  bottom  of  the  detritus,  immediately  on  the  bed- 
rock. 

With  regard  to  the  geological  age  of  the  detrital  tin-deposits,  the 
rule  stated  for  gold  generally  obtains,  namely,  they  are  for  the  most 
part  diluvial,  yet  have  sometimes  been  formed  in  earlier  periods. 
Thus,  at  Flatten,  in  Bohemia,  a  tin-placer,  which  has  been  worked 
under  a  bedded  flow  of  basalt,  and  the  detrital  deposits  of  Annaberg 
in  Saxony,  which  underlie  the  basalt  of  the  Scheibenberg,  were 
doubtless  formed  in  Tertiary  times. 

The  original  or  root-deposits  of  tin  have  been  hitherto  quite  gen- 
erally considered  as  very  old  formations,  connected  with  the  erup- 
tions of  granite  and  felsite-porphyry. 

Recently,  however,  tin  has  been  found  in  the  Mesozoic  limestones 
of  Campiglio  Maritima ;  and  it  has  been  shown,  moreover,  that  the 
root-deposits  of  tin  in  Mexico  and  Bolivia  occur  in  trachytes  and 
andesites,  erupted  during  the  Cretaceous  or  Eocene.  Dr.  A.  W. 
Stelzner  has  recently  published  a  notice  of  the  latter  occurrence,* 
and  promised  a  more  elaborate  description.  He  says  (p.  533) : 

'*  Th<5  part  played  in  geological  history  by  the  tin-ore  of  Bolivia,  contrasts  sharply 
with  that  which  has  been  observed  in  the  Erzgebirge  of  Saxony  and  Bohemia,  and 
in  Brittany,  Cornwall,  East  India,  Australia,  Tasmania,  and  the  United  States  of 
America,  and  which  has  hitherto  been  willingly  regarded  as  the  exclusive  method 
of  tin-occurrence.  The  Bolivian  tin-ore  does  not  constitute  aureoles  surrounding 
plutonic  granite,  and  characterized  by  the  contemporaneous  presence  of  minerals 
containing  boron  and  fluorine.  On  the  contrary,  it  can  only  be  considered  as  pro- 
duced, simultaneously  with  precious  silver-ores  and  sulphides  of  copper,  iron,  lead 
and  zinc,  by  precipitation  from  mineral  springs,  which  were  connected  in  point  of 
time,  and  perhaps  also  as  effects,  with  outflows  of  Cretaceous  or  Lower  Tertiary 
volcanic  rocks." 

c..  Hysteromorphous  Deposits  of  the  Older  Geological  Formations. 

Twenty-five  years  ago,  at  a  time  when  no  deposits  of  this  kind 
were  known,  in  an  article  on  the  continuance  of  ore-deposits  (espec- 
ially of  gold)  in  depth, f  I  prophesied  their  discovery.  They  have 
since  been  observed  in  different  gold-districts.  I  refer  to  the  charac- 
teristic secondary  deposits  in  quartz  conglomerates,  indicated  by  their 
stratigraphical  positions  and  their  contained  fossils  to  be  of  consid- 
erable geological  age.  Such  occurrences  are  often  called  simply 
cement-beds,  as  are  the  conglomerates  of  cemented  gravel  in  recent 
placers ;  and  it  is  difficult  in  cases  where,  as  in  Australia,  this 

*  Zeitsch.  d.  deutsch.  geol.  Gesellsch.,  xliv.,  1892,  p.  531. 
f  Oeslerr.  Zeitsch  /.  B.  u.  H.  W,  xv.,  1867. 


THE   GENESIS   OF   ORE-DEPOSITS.  147 

term  is  frequent,*  to  infer  the  age  of  the  corresponding  conglome- 
rates. It  is,  however,  in  some  cases  unquestionable  that  these 
cements  actually  represent  old  formations — chiefly  Palaeozoic — and 
are  therefore  hysteromorphic  products  from  still  older  primitive 
deposits. 

Deadwood,  Dakota. — One  of  the  best  described  occurrences  is  that 
of  Deadwood  and  Blacktail  gulches,  in  the  Black  Hills  of  Dakota.f 
It  is  a  conglomerate  bed,  passing  upwards  into  sandstone,  and  belong- 
ing, according  to  the  contained  fossils,  to  the  Potsdam  sandstone 
(Cambrian).  It  is  by  no  means  a  river-deposit;  on  the  contrary,  the 
fossils  indicate  a  shallow  marine  basin.  The  series  lies  very  flat  upon 
crystalline  schists ;  is  at  most  100  feet  (30  meters)  thick,  and  is  cov- 
ered by  a  layer  of  porphyry,  which  has  most  probably  protected  it 
from  erosion.  Fig.  100,  a  section  given  by  Mr.  Devereux  (L  c.,  p. 
468),  shows  how  the  deposit  is  exposed  and  rendered  accessible  on 
the  sides  of  Deadwood  and  Blacktail  gulches,  which  cut  through 
into  the  underlying  schists, 

The  conglomerates  of  pebbles  of  quartz,  schist,  and  hematite 
which  lie  at  the  base  of  this  Cambrian  series  carry  partly  coarse 
gold,  under  such  circumstances  that  there  can  be  no  doubt  of  its 
secondary  origin.  It  came  probably  from  the  Homestake  vein  near 
by.  The  auriferous  detritus  is  about  2  meters  (6.6  feet)  thick,  and 
the  portions  next  to  the  underlying  rock  are  the  richest ;  so  we  have 
here  the  relation  of  the  "  true  bed-rock."  If  my  theory  be  correct, 
that  the  gold  reached  this  position  by  sinking  through  the  lighter 
detritus,  it  might  be  said  that  the  gold  was  deposited  not  with,  but 
after,  the  detritus,  and  consequently  that  the  Cambrian  fossils  do  not 
prove  the  Cambrian  age  of  the  gold-deposition.  Such  an  objection 
might  perhaps  have  weight  in  other  cases  of  the  kind,  but  in  this 
case,  the  bed  being  covered  by  a  porphyry  overflow,  and  hence 
not  at  all  exposed  to  later  deposits,  the  objection  has  no  force. 

The  Black  Hills  contain  representatives  of  the  three  principal 
types  of  gold-occurrence,  namely,  gold-bearing  veins  and  ancient  and 
recent  detrital  deposits.  The  paper  of  Mr,  Devereux  is  also  very 
interesting  in  other  respects — for  instance,  with  regard  to  the  expla- 
nation of  the  differing  fineness  of  vein-  and  detrital-gold,  and 
with  regard  to  the  traces  of  chemical  action  in  the  detrital  de- 
posits. 

*  See,  for  example,  Mr.  Lock's  Gold,  etc.,  already  cited. 

f  W.  B.  Devereux,  uThe  Occurrence  of  Gold  in  the  Potsdam  Formation,  Black 
Hills,"  Trans.  A.  I.  M.  E.t  1882,  x.,  465, 


148  THE   GENESIS   OF   ORE-DEPOSITS. 

Australasia. — The  data  from  Australasia  concerning  this  class  of 
deposits  are  less  conclusive.  In  1876  Wilkinson  observed  in  the 
Talhawang  district  of  New  South  Wales  that  the  Tertiary  detrital 
deposits  received  their  gold  from  Carboniferous  conglomerates. 
These  conglomerates  were  associated  with  sandstones  and  slates,  in 
which  occurred  a  fossil  plant  peculiar  to  the  Carboniferous  of  New 
South  Wales.  The  gold  occurred  in  pretty  coarse,  roundect  grains, 
and  on  one  occasion  a  nugget  was  found  weighing  5  ounces  (155 
grammes).  Similar  conditions  are  said  to  obtain  in  the  Hawkesbury 
rocks,  at  the  North  Shore,  Sydney,  at  Govett's  Leap,  and  in  the 
conglomerates  of  the  Coal-Measures  in  the  southern  district.  Gold 
is  also  reported  in  the  Coal-Measures  at  Peak  Downs  in  Queensland, 
near  Hobart  Town  in  Tasmania,  and  in  New  Zealand.* 

The  question,  whether  these  deposits  of  gold  were  really  made 
simultaneously  with  that  of  the  detritus  in  the  Carboniferous  period, 
may  be  decided  by  the  circumstance  that  the  conglomerates  are  or 
are  not  covered  by  Carboniferous  strata.  In  the  latter  ease,  it  is 
possible  that  the  gold  may  have  sunk  into  the  gravel  at  a  later 
period. 

South  Africa. — In  South  Africa,  at  Witwatersrand  in  the  Trans- 
vaal, ancient  detrital  deposits  have  yielded  a  considerable  gold- 
production.  According  to  E.  Cohen, f  the  Witwatersrand  consists 
of  sandstones  (which  resemble  closely  that  of  Table  mountains  at 
the  Cape  of  Good  Hope)  and  dolomites  of  high  age — undoubtedly 
Paleozoic.  Conglomerates  of  the  same  age,  intercalated  among 
these  strata,  occur  in  the  vicinity  of  Johannesburg  in  several  nearly 
parallel  outcrops,  and  are  for  certain  distances  tolerably  rich  in  gold. 
They  are  composed  mostly  of  quartz  pebbles,  sometimes  with  frag- 
ments not  entirely  rounded,  which  are  united  by  a  strong,  ferrugin- 
ous, arkose-like  cement.  The  quartz  pebbles  are  sometimes  porous 
and  impregnated  with  hydrated  ferric  oxide,  thus  presenting  the 
peculiar  corroded  appearance  so  characteristic  of  auriferous  quartz. 
The  gold  occurs  chiefly  in  the  cement,  immediately  next  to  the 
pebbles.  It  is  mostly  coarse-grained,  and  sometimes  even  crystal- 
line. The  latter  circumstance  has  raised  the  question  whether  the 
gold  has  not  here  been  chemically  precipitated,  and  hence,  whether 
these  are  detritus-deposits  at  all.  My  standpoint  in  this  discussion, 
as  I  have  remarked  at  the  end  of  the  section  on  chemical  effects- 

*  Lock's  Gold,  etc.,  pp.  515,  516.  See  also  R.  Daubree's  "  Note  on  Certain  Modes 
of  Occurrence  of  Gold  in  Australia,"  Quart.  Jour.  Geol.  Soc.,  1878,  xxxiv  ,  p.  435. 
f  "  Goldfiihr  Conglom.  in  Sudafrika."  Mitth.  d.  naturw.Ver.  f.  Neupommern,  etc. 


THE   GENESIS   OF   ORE-DEPOSITS.  149 

in  the  upper  region,  is  like  that  of  E.  Cohen.  I  do  not  deny  the 
presence  of  chemical  influences  in  the  detrital  deposits,  although  I 
have  personally  not  happened  upon  them.  So  far  as  I  can  judge 
from  the  treatises  of  A.  R.  Sawyer*  and  Charles  A.  Alford,f  and 
from  a  specimen  of  the  Witwatersrand  conglomerate,  kindly  sent  to 
me  by  A.  H.  Halden  of  Pietersburg,  it  is  my  opinion  that  the  gold 
was  mechanically  brought  into  the  conglomerates  from  still  older 
auriferous  quartz- veins  occurring  in  the  rocks  which  form  the  basis 
of  this  Palaeozoic  formation ;  and  since  the  idea  of  a  later  entrance 
of  the  gold  is  excluded  by  the  almost  vertical  position  of  the  con- 
glomerate beds  near  Johannesburg,  I  suppose  the  gold  to  have  been 
deposited  at  the  same  time  as  the  detritus.  The  'greater  part  of  the 
gold,  as  has  been  said,  occurs  in  the  cement.  There  are  no  vein- 
like  deposits  whatever  in  the  conglomerate ;  and  the  only  chemical 
changes  which  could  be  presumed  are  confined  to  the  decomposition 
of  pyrites  and  the  segregation  of  its  contained  gold. 

According  to  a  foot-note  ip  Phillips's  Treatise  on  Ore-Deposits 
(p.  2),  gold  is  washed  out  of  granular  conglomerates  of  the  Lower 
Carboniferous  at  Besseges,  Department  du  Gard,  France. 

Bohemia. — In  the  region  of  Trautenau,  in  Bohemia,  I  observed 
at  Gabersdorf  and  Goldenols  considerable  traces  of  ancient  placer- 
mining,  partly  in  the  valley-bottom,  partly  on  the  slope,  which 
consisted  of  old  Permian  and  Carboniferous  conglomerates.  These 
remains  looked  exactly  like  other  gold-workings  in  Bohemia,  and  I 
could  only  explain  their  situation  by  supposing  that  this  was  another 
case  of  auriferous  Palaeozoic  detritus.  The  same  may  be  said  of 
another  enigmatical  gold-occurrence,  at  Stupna  in  Bohemia,  where 
in  1593  a  gold  of  unusual  fineness  (0.954)  for  Bohemia  was  produced, 
and  must  have  come  from  a  detrital  deposit.  The  ancient  miners 
penetrated  through  beddfd  flows  of  melaphyre.  The  waste-dumps 
are  composed  of  pebbles  from  Permian  conglomerates.  It  is  there- 
fore possible  that  these  mines  were  operated  upon  auriferous  Per- 
mian conglomerates.  J 

*  "  The  Witwatersrand  Gold-field."  Trait*.  N.  Sta/ordsh.,  Inst.  M.  and  Meek.  E. 
1839. 

f  Geological  Features  of  the  Transvaal,  London,  1891. 

J  F.  Posepny,  "  Ueber  einige  wenig  bekannte,  alte  Goldbergbaue  Bohmens." 
Oesterr.  z.f.  B.  u.  H.  W.,  xxxvii.,  1889. 


DESCRIPTION  OF  FIGURES. 

Fig.  1. — Erosion  of  a  channel  in  rock-salt,  at  Maros  Ujva>, 
Transylvania.  I,  impermeable  rock  ;  S,  rock-salt ;  H,  hydrostatic 
head  of  vadose  circulation. 

Figs.  2  and  3. — Course  of  vadose  circulation,  as  affected  by  the 
nature  of  the  rocks.  S,  soluble,  I,  insoluble  rock  ;  H,  hydrostatic 
head  ;  a,  entrance,  z,  outlet ;  a  b  c  z,  rTatural  curve  of  water-circula- 
tion, if  I  did  not  intervene ;  a  d  z,  actual  path  under  or  over  I. 

Fig.  4. — Geode  of  JEisenopal  (jasp-opal),  showing  the  filling  of  a 
cavity  in  which  air  or  gas  is  present,  besides  the  liquid. 

Fig.  5. — Diagrammatic  representation  of  deposits  in  a  limestone 
cavern.  (Deposits  white ;  empty  space,  black.) 

Fig.  6. — Division  of  ground-water  by  fissures  and  permeable 
strata. 

Fig.  7. — Conventional  representation  of  an  artesian  well. 

Fig.  8. — Spring-mounds  at  Arczo  near  Korond,  in  Transylvania. 

Fig.  9. — Upward  erosions  in  building-stone  in  the  walled  pit  of 
a  sprkig  at  Bourbonne-les-Bains. 


Fig,  I 


Fig.  2 


Fig.  3 


DESCRIPTION  OF  FIGURES. 

Fig.  10. — Deposition  of  cinnabar  and  opal  in  basalt  at  Sulphur 
Bank,  Cal.  Sketch  at  the  surface  by  F.  Posepny. 

Fig.  11. — Similar  deposition  at  the  same  mine,  in  sandstone,  at 
greater  depth  (J.  Le  Conte). 

Fig.  12. — Carlsbad  Sprudelstein.  j. 

Fig.  13. — Pisolite  with  pyrite  crusts,  from  Hammam  Mesoutine. 

Figs.  14,  15  and  16. — Pisolites  formed  by  dripping  solutions  at 
Offenbanya. 

Fig.  17. — Sphere-ores,  a  correction  of  the  illustrations  of  Cotta 
(Erzl.  Lehre,  I.,  33)  and  Daubree  (Les  eaux  aux  tpoques  anciennes, 
p.  64). 

Fig.  18. — Gold   specimen  from  the  Katrontza  ore-body,  Veres- 


Fig.  19. — A  crusted  rock-nucleus,  from  Raibl. 

Fig.  20. — Boiler-scale. 

Figs.  21  and  22. — Fragments  of  rock  and  older  crusts,  surrounded 
by  later  crusts,  from  Zellerfeld  (J.  C.  L.  Schmidt). 

Fig.  24. — Gold- aggregates,  surrounded  by  crusts  of  calcite,  rhodo- 
nite, siderite  and  quartz,  from  the  Rdkosi  Mangan  ore-body,  Veres- 
patak. 


Fig.22 


DESCRIPTION  OF  FIGURES. 

Figs.  25,  26,  27  and  28. — Sections  of  stalactites  of  galena,  blende 
and  pyrite,  so-called  " pipe-ores,"  with  hollow  axis,  from  Raibl. 

Fig.  29. — Section  of  rhodonite  stalactites,  with  axis  of  gold -aggre- 
gates, from  the  Hungarian  National  Museum. 

Fig.  30. — View  of  the  same. 

Fig.  31. — Section  of  a  similar  stalactite  in  the  author's  possession, 
from  the  Rakosi  Mangan  ore-body.  Enlarged  to  twice  the  natural 
size. 

Figs.  32,  33,  34,  35. — Sections  of  ore-channels  in  the  limestone  of 

O  ft 

the  Valle  mines,  Missouri  (J.  R.  Gage). 


Fig.25 


Fig.29 


Bradley  f  .Poatet,  Engr't,  N.  K 


DESCRIPTION  OF  FIGURES. 

FIG.  3fi. — Plan  showing  gold-bearing  veinlets,  striking  E.  to  W., 
in  granite  (berezite)  striking  N.  to  S.,  at  Berezov. 

FIG.  37. — Network  of  veins  and  vein-clay-slates  in  the  Clausthal 
district.  Localities:  a,  Lautensthal ;  6,  Bockwiese;  c,  Festenberg; 
dj  Ober-Schulenberg ;  e,  Wildemann;  /,  Zellerfeld;  g,  Clausthal. 

FIG.  38. — Network  of  veins  and  Euschel  in  the  St.  Andreasberg 
district.  Ruschel:  ab,  Neufang;  a  c,  Edellent;  dfe,  Silberberg; 
fg  h,  Abendroth  Veins:  1 1,  Samson  (i,  Samson  shaft);  k  k,  Berg- 
man nstrost. 

FIG.  39. — Section  through  the  Franz  Josef  shaft,  Przibram,  Bo- 
hemia. A  B,  sea-level,  heights  above  and  below  which  are  given 
in  meters  on  the  left.  The  Roman  numerals  on  the  right  indicate 
the  vein-levels,  a,  post-Cambrian  slates;  6,  Cambrian  sandstone; 
c,  c,  faulted  stratum  of  adinole;  </,  d,  diorite  dikes;  m,  Martyr 
vein ;  u  u,  Marie  Hilf  vein ;  v,  v,  v,  Sefcin  vein ;  w  w,  West-dip- 
ping vein  ;  s  s,  Franz  Josef  shaft. 


BraMey  $  Pwt«t,  Etigr't,  X.  Y, 


DESCRIPTION  OF  FIGURES. 

FIG.  40. — Ideal  section  through  Bohutin,  near  Prsibram.  a,  Cam- 
brian sandstone;  6,  pre-Carabrian  schists;  c,  granite;  d,  main  fault- 
fissure  ;  e  e,  diorite  dikes.  (NoTE :  At  Przibram  itself  the  pre-Cam- 
brian  schists  constitute  the  hanging-wall  of  the  main  fault-fissure  to 
the  entire  depth  of  the  mines — about  1100  meters,  or  3600  feet.) 

FIG.  41.- — Diagrammatic  representation  of  the  structure  of  the 
Verespatak  ore-bodies  (Volbura),  showing  the  ore  replacing  the 
washed-out  cement  of  a  breccia,  mostly  of  porphyritic  fragments. 

FIG.  42. — The  same,  only  conglomerate  instead  of  breccia. 

FIG.  43. — Vertical  S.  to  N.  section  through  the  Yulkoj  mines, 
showing  the  supra-ppsition  of  andesite  upon  the  shaly  sandstone. 
a  a,  Nepomuk  adit^  6,  sandstone;  c,  andesite;  d,  Corabia  open- 
workings;  e,  Jeruga  adit;  /,  Peter- Paul  adit;  gy  Hermann  adit. 

FIG.  44. — Vertical  E.  to  W.  section  through  the  gold-mines  of 
Botesiu  and  Vulkoj.  A,  Botesiu;  B,  Vulkoj  ;  a,  Nepomuk  adit; 
6,  sandstone;  c,  andesite;  d,  Corabia  open-workings;  j,  Jeruga 
vein. 


Fig.  40 


Fig.  41 


f^l^'r^' 

Jy  • '  ** x 

Fig.  42 


Fig.  43 


Bradley  ,fctfte»*M,  Bngr'*t  #•£, 


DESCRIPTION  OF  FIGURES. 

FIG.  45. — Section  in  fourth  level  of  Peter  Stehend  vein,  Freiberg. 
«,  decomposed  country-rock;  6,  quartz,  with  brown-spar,  pyrites, 
blende,  and  silver-ores.  (G.  A.  Von  Weissenbach,  No.  2  in  his 
work.) 

FIG.  46. — Section  on  third  level  of  Adlerfliigel  Stehend  vein, 
Freiberg,  a,  gneiss  fragments ;  6,  older  vein-formation ;  c,  later 
quartz  vein-matter;  d,  gneiss.  (Weissenbach,  No.  21  in  his  work.) 

FIG.  47. — Section  on  third  level  of  Gnade  Gottes  Stehend  vein, 
Freiberg.  (Weissenbach,  No.  22.) 

FIG.  48. — Section  on  thirteenth  level  of  Adalbert  Liegend  vein, 
Przibram.  a,  galena  and  calcite  ;  6  (or,  more  precisely,  the  irregu- 
lar mass  shown  to  the  right  of  6),  zincblende;  c,  sandstone.  (J. 
Zadrazil,  No.  52.) 

FIG.  49. — Section  on  thirteenth  level  of  Adalbert  master-lode, 
Przibram.  a,  siderite;  6,  calcite;  c,  quartz;  d,  galena;  e,  diorite. 
(J.  Zadrazil,  No.  5.) 

FIG.  50. — Section  on  twenty-ninth  level  of  Adalbert  master-lode, 
Przibram.  a,  calcite;  6, silicified  (verquarzte)  vein-matter;  c,  quartz; 

d,  diorite.     (J.  Zadrazil,  No.  21.) 

FIG.  51. — Section  on  adit  of  Hildebrand  vein,  Joachimsthal.  a, 
mica-slate;  6,  dolomite;  c,  c,  proustite;  d,  dolomite  with  pyrite; 

e,  uranite.     (J.  Nemecek,  No.  11.) 

FIG.  52. — Section  on  tenth  level  of  Junghauerzechen  vein,  Joa- 
chimsthal. a,  a,  dolomite  and  calcite;  6,  6,  mica-schist;  c,  basalt- 
wacke;  d,  chalco-pyrite ;  e,  proustite.  (J.  Nemecek,  No.  5.) 


DESCRIPTION  OF  FIGURES. 

FIG.  53. — Specimen  from  the  Drei  Prinzen  Spat  vein,  in  the 
eighth  level  of  the  Churprinz  Friedrich  August  mine,  Freiberg, 
Saxony;  ^  nat.  size;  a,  quartz  with  disseminated  galena  and  blende, 
indistinctly  crustified — from  the  older  vein  ;  6,  fluorite  with  quartz; 
c,  barite  in  thin  crusts ;  d,  gray  earthy  mass  of  the  later  vein,  very 
distinctly  crustified  ;  e,  the  latest  fault-fissure. 

FIG.  54. — Copper-deposit  at  Prettau  in  Tyrol.  Sketch  of  the  roof 
of  the  Ottilie  level. 

FIG.  55, — Ditto;  side  of  the  same  level. 

FIG.  56. — Ditto;  vertical  section  in  the  plane  of  the  pitch,  which 
descends  nearly  westward,  the  course  of  the  strata  being  E.  to  W., 
and  the  dip  steep  to  South.  Adits  and  levels :  a,  Peter;  6,  Jacob ;  c, 
Marx;  d,  Johanu;  e,  Kristof;  /,  Nikolaus;  g,  Ignatz.  The  three 
levels  below  g  are  the  Ottilie,  Karl,  and  Hugo. 

FIG.  57. — Ditto ;  horizontal  projection,  showing  approximately 
the  position  of  the  ore-bodies  on  the  different  levels :  a  to  g  as  in 
Fig.  56;  x  y,  strike;  y  w,  true  dip  of  strata;  y  z,  pitch  of  ore- 
shoot. 


DESCRIPTION  OF  FIGURES. 

FIG.  58. — Surface-geology  of  the  vicinity  of  the  Comstock  lode. 
B,  basalt ;  L  H  A,  later  hornblende-andesite ;  A  A,  augite-andesite ; 
E  H  A,  earlier  hornblende-andesite;  L  D  6,  later  diabase  (black 
dike) ;  E  D  6,  earlier  diabase;  Q  P,  quartz-porphyry  ;  M  D  r,  met- 
amorphosed diorite  ;  P  D  e,  porphyritic  diorite ;  G  D  r,  granular  dio- 
rite ;  M,  metamorphic  rocks ;  G,  granite.  (G.  F.  Becker.) 

FIG.  59. — Vertical  cross-section  through  Union  shaft.  (G.  F. 
Becker.) 

FIG.  60. — Vertical  cross-section  through  C.  and  C.  shaft.  (G.  F. 
Becker.) 

FIG.  61. — Vertical  cross-section  through  Yellow  Jacket  shaft. 
(G.  F.  Becker.) 

FIG.  62. — Vertical  cross-section  through  Belcher  shaft.  (G.  F. 
Becker.) 

FIG.  63.— Vertical  section  on  line  of  Sutro  tunnel.  I,  II,  III, 
and  IV,  Sutro  tunnel  shafts ;  s  s,  lines  of  solfataric  action  ;  v,  vein- 
material.  (G.  F.  Becker.) 


ty-$  Poates,  Engr's,.N.T. 


DESCRIPTION  OF  FIGURES. 

FIG.  64. — Vertical  E.  and  W.  section  through  the  mines  of  Yalle 
Sacca,  near  Rezbanya,.  Hungary,  a,  sandstone ;  6,  Jurassic  lime- 
stone ;  c,  Liassic  limestone  ;  dd,  crystalline  limestone;  e,  syenite;  /, 
3d  adit;  g,  4th  adit;  h,  new  Anton  adit;  i,  Juliana  ore-body;  k, 
Marianna  ore-body;  /,  Anton  ore-body;  mm,  parallel  intercalated 
dike;  rm,  Rischenstein  ore  body  ;  oo,  dikes. 

FIG.  65. — Vertical  longitudinal  section  of  Reiehenstein  ore- 
body,  Valle  Sacca,  Hungary,  rm,  ore-body  ;  6,  limestone ;  d,  1st 
adit ;  e,  2d  adit :  /,  3d  adit. 

FIG.  66. — Diagram  showing  the  S.  W.  pitch  of  the  Reichenstein 
ore-body,  the  dikes  dipping  W.  x  y,  course  of  dikes;  x  w,  dip  of 
dikes;  x  z,  pitch  of  are-shoot. 

FIG.  67. — Vertical  N.  and  S.  cross-section  of  the  Government 
mine  at  Raibl,  Carinthia.  a,  Raibl  slates;  6,  ore-bearing  lime- 
stone. Adits  :  c,  Johann  ;  d,  Frauen  ;  e,  Sebastian  ;  /,  Franz,  II., 
IV.,  VI.  and  VII.,  positions  of  levels  numbered  upwards  from 
Johann  adit. 

FIG.  68. — Vertical  N.  and  S.  section  through  the  Struggl  mine  at 
Raibl.  a,  slate  ;  6,  ore-bearing  limestone ;  /,  Franz  adit ;  gy  Ein- 
siedl  level. 

FIG.  69.— Faulting  of  the  contact  by  a  "  Blutt."  a,  slate ;  6, 
limestone. 

FIG.  70. — Vertical  N.  and  S.  cross-section  through  the  Benyes 
mine,  Rodna,  Transylvania,  a,  mica-slate ;  b,  andesite ;  c,  lime- 
stone. Adits:  d,  Amalia;  ey  Zap  Peter;  /,  Anton  ;  g,  Nepomuk  ; 
h,  Teresia. 

FIG.  71. — Section  through  the  "  New  Lead-Mass/7  in  Mt. 
Ambree,  Offenbanya,  Transylvania,  a,  mica-slate;  6,  andesite;  c, 
limestone.  Levels  :  c?,  Segen  Gottes  ;  e,  Gltick  auf ;  /,  ore-shoot. 


DESCRIPTION  OF  FIGURES. 

FIG.  72. — Face  of  level  on  the  JosepMblatt,  at  Raibl,  where  the 
ores  occur  in  the  country-rock. 

FIG.  73.— Vertical  E.  and  W.  section  through  the  McKean  shaft, 
Iron  Hill,  Leadville,  Colo.  W.  P.,  white  porphyry ;  B.  L.,  blue 
limestone;  G.  P.,  gray  porphyry;  W.  L.,  white  limestone;  L.  Q., 
lower  quartzite ;  G.,  granite.  (A.  A.  Blow.) 

FIG.  74. — Sections  from  the  Red  Mountain  district,  Colo.  A., 
andesite ;  P.  Q,,  pink  quartzite  ;  L.,  limestone ;  L.  Q.,  lower  quartz- 
ite; a,  Batavia  shaft;  a&,  Jackson  tunnel;  c,  adit;  oo,  ore.  (G.  E. 
Kedzie.) 

FIG.'  75. — Section  across  Longfellow  Hill  and  Chase  Creek,  Clif- 
ton district,  Arizona.  A,  Longfellow  Hill;  B,  Chase  Creek;  aa, 
felsite;  6,  limestone;  <?,  sandstone;  d,  porphyry;  e,  upper  adit;  /, 
deep  adit.  (A.  F.  Wendt.) 

FIG.  76. — Ideal  sections  at  Eureka,  Nevada.  A,  Ruby  Hill;  a, 
Prospect  Mountain  quartzite;  6,  crushed  limestone;  e,  limestone  ,  d, 
shale;  €,  stratified  limestone;  /,  Secret  Cafion  shale;  g,  Hamburg 
limestone;  i,  Logan  shaft;  p,  Lawton  shaft.  (J.  S.  Curtis.) 

FIG.  77. — Combined  section  at  Eureka  for  comparison  with  Fig. 
76.  a,  b,  c,  d,  ef  /,  as  above ;  k,  Windsail  shaft ;  I,  Bell  shaft ;  m, 
Richmond  shaft;  x  y,  east  ore-body;  VII.,  Richmond  7th  level. 
(J.  S.  Curtis.) 

FIG.  78.— Sketch  of  face  of  310  feet  level.  Old  Telegraph  mine, 
Utah,  showing  texture  of  the  filling  (altered  to  cerussite).  a,  hang- 
ing-wall clay  ;  6,  quartz;  c,  quartzite. 

FIG.  79. — Section  from  the  lead-region  of  Wisconsin,  in  the  neigh- 
borhood of  Dubuque,  Iowa.  (J.  D.  Whitney.) 


Mradley  §  .tyatet,  Jsaigr's,  . 


DESCRIPTION  OF  FIGURES. 

FIG.  80. — Plan  of  ore-deposits  at  Wallerfangen  and  St.  Avoid, 
near  Saar  Louis.  (C.  Simon.) 

FIG.  81. — Cross-section  of  81.     H,  hanging-wall;  F,  foot-wall. 

FIG.  82. — Cross-section  of  the  Mechernich  deposits,  showing 
irregular  faulting  of  the  Knoten  sandstone  beds. 

FIG.  83. — Cross-section  of  the  Vesuv  mine,  Freihung,  Bavaria, 
a,  Keuper  clay  ;  6,  variegated  sandstone ;  c,  ore-beds ;  d,  engine- 
shaft. 

FIG.  84. — Section  of  a  tree-stem,  replaced  with  galenite,  from 
Freihung. 

FIG.  85.  Calamine  veinlets  in  the  limestone  at  Raibl ;  a,  lime- 
stone. 

FIG.  86. — Cellular  calamine  of  Raibl. 

FIG.  87. — Section  through  the  Laurium  district,  Greece;  a,  lime- 
stone ;  b,  schist ;  c,  Hilarion  shaft.  (A.  Cordelia.) 

FIG.  88. — Section  through  the  Laurium  district ;  «,  limestone  ;  6, 
schist;  d,  porphyry  dikes.  (A.  Huot.) 

FIG.  89. — Limonite-deposit  in  West  Cumberland  ;  a,  millstone 
grist;  6,  mountain  limestone;  c,  Silurian  schist.  Hematite  in  place. 
(J.  D.  Kendall). 

FIG.  90. — Bohneisenstein-deposit  of  Wochein,  Carniola ;  «,  lime- 
stone ;  bj  iron-ore.  (A.  v.  Morlot.) 


Sradley  f  POctto,  Engr'a,  A:  % 


DESCRIPTION  OF  FIGURES. 

FIG.  91. — Tin-vein  in  Cornwall,  with  pseudomorphs  of  cassiter- 
ite  after  feldspar  in  the  granite  country-rock.  (C.  Le  Neve  Foster.) 

FIG.  92. — Tin-vein  in  Cornwall,  showing  "capel"  or  altered 
"killas"  country-rock.  (C.  Le  Neve  Foster,) 

FIG.  93. — Impregnation  of  the  granite  with  tin-ore  at  East  Wheal 
Lovell,  Cornwall.  (C.  Le  Neve  Foster.) 

FIG.  94. — Specimens  of  ore  from  the  Kongens  mine  at  Roras, 
Norway.  (Th.  Kjerulf.) 

FIG.  95. — Specimen  of  ore  from  the  Mug  mine,  Trondhjem,  Nor- 
way ;  a,  pyrrhotite ;  6,  mica ;  c,  quartz ;  d,  chalcopyrite.  (Th. 
Kjerulf.) 

FIG.  96. — Polished  section  of  ore  from  Ammeberg,  Sweden. 

FJG.  97. — Ditto,  showing  leaf-silver  in  fissures  in  zinc-blende. 

FiG.  98. — Section  through  the  Copper  Falls  mine,  Lake  Superior  ; 
a,  trap  ;  6,  ash-bed  at  depth  of  80  feet ;  c,  amygdaloid  ;  d,  sand- 
stone at  depth  of  420  feet. 

FIG.  99. — Nagynyerges  vein  at  Kisbdnya,  Transylvania. 

FIG.  100. — Section  through  Palaeozoic  detrital  gold-deposit  of  the 
Black  Hills;  a,  porphyry;  6,  schist;  d,  Potsdam  (old  contact-lines 
dotted) ;  e,  cement-mines  ;  ffy  placers,  the  one  on  the  left  in  the  draw- 
ing being  in  Dead  wood  gulch  at  Central  City  ;  the  one  on  the  right, 
in  Blacktail  gulch.  (Devereux.) 


174  THE   GENESIS   OF   ORE-DEPOSITS. 


DISCUSSION 

AT  THE  CHICAGO  MEETING,  AUGUST,  1893,  INCLUDING  COM- 
MUNICATIONS SUBSEQUENTLY  RECEIVED. 

R.  W.  RAYMOND,  New  York  City  :  On  page  37,  the  Fahrenheit 
degrees  are  incorrectly  given.  The  centigrade  degrees  are  correct, 
except  as  to  No.  8  (Ophir),  which  should  be  21.1°  C. 

W.  P.  BLAKE,  Shullsburg,  Wis. :  I  desire  to  express  my  admi- 
ration of  Prof.  Posepny's  memoir,  and  particularly  of  the  charming 
manner  and  spirit  of  the  introduction. 

With  respect  to  his  mention  of  the  ore-deposits  of  Missouri  and 
Wisconsin,  reference  may  be  made  to  my  paper  presented  at  this 
meeting  (Trans.,  xxii.,  621),  showing  the  existence  of  dislocations 
and  breaks  in  the  bedding,  and  their  apparent  close  relation  with 
the  localization  of  the  ore-deposits  as  claimed  by  Dr.  James  G. 
Percival,  and  also  so  claimed  by  Dr.  Jenney  in  his  paper  before  us 
(Trans.,  xxii.,  171).  I  have  in  my  paper  given  reasons  for  believing 
that  the  zinc-  and  lead- ores  in  the  strata  above  the  compact  Trenton 
limestones  were  formed  by  lateral  secretion  and  concentration  from 
above  downwards,  substantially  as  shown  by  Prof.  J.  D.  Whitney, 
and  not  by  the  ascent  of  solutions  through  the  fissures,  as  Prof. 
Posepny  (p.  108)  seems  inclined  to  believe. 

In  regard  to  the  contemporaneity  of  the  ore  and  the  rocks,  and 
in  favor  of  a  later  introduction  of  ore  through  fault-fissures,  Prof. 
Posepny  (p.  114)  cites  the  influence  of  these  fissures.  In  my  paper, 
already  referred  to,  I  have  endeavored  to  show  how  faults  may  have 
influenced  the  deposition  of  ore  without  being  themselves  channels 
for  the  flow  of  mineral  solutions,  and  how  they  may  have  caused  the 
contemporaneous  formation  of  metallic  sulphides  from  sea-water  in 
the  body  of  a  forming  rock ;  the  faulting  fissure  being  formed  at  an 
early  period  in  the  foundation  rocks,  and  probably  continuing  to 
be  a  plane  of  break  and  movement  in  the  deposits  of  later  forma- 
tion. 

ARTHUR  WINSLOW,  Jefferson  City,  Mo. :  The  results  of  exten- 
sive and  long  continued  studies,  such  as  are  here  presented  by  Prof. 


THE   GENESIS   OF   ORE-DEPOSITS.  175 

Posepny,  deserve  most  careful  consideration  before  one  should 
undertake  to  criticise  the  general  conclusions  or  judge  of  the  broader 
bearings  of  his  work.  I  shall  not  attempt  anything  of  the  kind. 
The  remarks  made  by  me  (Trans.,  xxii.,  634,  735)  in  the  discussions 
of  Mr.  Emmons's  and  Dr.  Jenney's  papers,  presented  at  this  meeting, 
are  to  a  great  extent  applicable  here;  but  I  wish  to  add  a  few  more 
words  bearing  directly  upon  Prof.  Posepny's  statements  concerning 
the  Missouri  and  Wisconsin  ores. 

On  page  107  he  says  that  while  the  deposits,  away  from  the  granite 
and  porphyry  "  islands  "  of  southeastern  Missouri  consist  chiefly  of 
lead-  and  zinc-ores,  "other  metals,  such  as  copper,  cobalt,  and  nickel, 
occur  as  the  Archean  foundation-rocks  are  approached."  This  cir- 
cumstance, he  says,  is  "an  indication  that  the  source  of  the  lead- 
deposits  also  is  to  be  sought  in  depth.'7  Whatever  may  be  the  value 
of  this  indication,  I  do  not  think  the  facts  as  stated  hold  generally. 
I  judge  that  Prof.  Posepny  reasons  from  his  observations  at  Mine 
La  Motte,  where  such  conditions  exist.  At  other  points,  however, 
these  changes  in  composition  are  not  observed  as  the  crystalline  rocks 
are  approached.  At  Doe  Run,  a  mine  recently  opened,  work  is 
prosecuted  along  the  old  water-worn  pre-Cambrian  surface  of  the 
Archean  granite,  among  the  conglomerate  boulders  themselves  ;  and 
few  or  no  copper-,  cobalt-,  or  nickel-ores  are  found.  Again  at 
other  localities,  in  St.  Genevieve,  Franklin,  Crawford  and  other 
counties,  copper-ores  occur  remote  from  any  granite  or  porphyry 
outcrops  and  well  above  the  basal  beds  of  the  Cambrian. 

With  reference  to  the  Wisconsin  deposits,  our  author  seems  to 
think  the  absence  of  ores,  in  the  great  thicknesses  of  limestones  and 
sandstones  which  underlie  the  productive  horizons,  by  no  means  con- 
clusive as  an  argument  against  their  deep-seated  source,  and  suggests 
that  the  solutions  may  have  come  up  through  a  passage  not  yet 
exposed,  and  even  that  fault-fissures  and  eruptive  dikes  may  exist 
which  have  not  been  discovered.  From  the  fact  that  he  refers  in 
this  connection  only  to  Whitney's  report  of  1862, 1  conclude  that  he 
has  not  had  access  to  the  later  and  more  exhaustive  works  of  Strong 
and  Chamberlin.  Perhaps  with  the  full  light  conveyed  by  these 
reports  and  accompanying  maps,  Prof.  Posepny  might  have  attached 
more  importance  to  the  objections  raised.  For  my  own  part  I  do 
not  see  how  such  a  passage  for  the  solutions  as  he  suggests  could 
possibly  exist  without  its  presence  having  been  revealed  and  its 
course  traced,  through  the  widespread  mining  and  exploring  which 


176  THE   GENESIS   OF   ORE-DEPOSITS. 

lias  been  conducted  in  this  region  during  the  past  seventy  years. 
Neither  do  I  yet  see  how  the  solutions  could  traverse  the  interven- 
ing great  thicknesses  of  water-soaked  sandstones  without  becoming 
diffused,  in  great  part  at  least.  The  failure  to  find  such  a  passage 
and  the  absence  of  the  ores  in  the  beds  assumed  to  have  been 
traversed,  though  evidence  of  a  negative  character,  is  so  strong 
that  it  becomes  of  almost  positive  value  in  support  of  the  theory  of 
lateral  segregation. 

T.  A.  RICKARD,  Denver,  Colo. :  The  distinguished  author  of  this 
paper  has  referred  to  the  Leadville  monograph  of  Emmons,  as 
"  epoch-making."  This  judgment  has  been  anticipated,  I  believe, 
by  most  of  us.  It  serves,  however,  very  well  to  recall  the  fact  that 
the  publication  of  that  particular  monograph  marked  the  high  tide 
of  the  lateral-secretion  theory,  which  owed  its  importance  more  to 
the  fact  of  its  acceptance  by  certain  distinguished  geologists  than  to 
its  incomplete  demonstration  by  Sandberger. 

What  Prof.  Posepny  said  of  the  work  of  our  American  geologist 
we  can  say,  with  even  greater  force,  of  his  present  contribution.  His 
dissection  of  the  theory  promulgated  by  Sandberger  is  most  effective. 
The  sympathies  of  the  miner  are  with  him  in  that  demolition  of  the 
lateral -secretion  theory ;  for  the  latter  was  an  explanation  which 
never  found  much  favor  underground,  with  the  miner,  but  had  its 
stronghold  in  its  own  particular  habitat,  the  professor's  sanctum. 
Here  I  would  throw  out  the  suggestion  to  my  fellow  mining  engi- 
neers, whose  business  is  to  observe  rather  than  to  theorize,  that  these 
distinguished  scientists  must,  after  all,  look  to  the  men  who  spend 
much  time  underground  for  the  accumulation  of  evidence  whereon 
to  found  their  hypotheses.  If  the  genesis  of  ore-deposits  is  to  be 
unravelled,  more  particularly  if  this  study  is  destined  to  be  capable 
of  further  practical  and  economic  application,  it  must  be  through  the 
gathering  of  facts  and  not  the  mere  building  of  theories.  Prof. 
Posepny  has  very  properly  pointed  out  that  Sandberger's  views 
gained  many  disciples  because  they  permitted  extensive  generaliza- 
tions to  be  made  above  ground,  and  in  comfort,  but  did  not  so  much 
require  a  descent  underground  and  the  making  of  observations  under 
conditions  of  discomfort.  Therefore,  I  would  say,  let  those  of  us 
who  have  the  opportunity  aid  in  the  elucidation  of  truth  by  the  coir 
lection  of  the  facts  and  observations  without  which  speculations  re- 
garding the  origin  and  formation  of  ore-deposits  are  worse  than  vain. 

Prof.   Posepny  emphasizes  the  fact  of  the  ascension  of  mineral 


THE   GENESIS   OF   ORE-DEPOSITS.  177 

solutions.  I  venture  to  suggest  that  these  terms — "ascending," 
"  lateral, "  and  "descending" — may  all  be  applied  to  mineral  solu- 
tions at  various  periods  and  under  various  conditions.  It  is  the 
great  fact  of  circulation  which  covers  all.  The  water  which  comes 
up  must  have  first  gone  down  ;  its  original  descent  was  as  necessary 
to  the  process  of  ore-formation  as  its  subsequent  ascent.  When  and 
where  in  its  journeying  it  became  a  solvent  and  when  and  where  it 
became  a  precipitant — that  is  what  the  miner  wants  to  know.  The 
ultimate  formation  of  an  ore-deposit  is  dependent  more  upon  condi- 
tions favoring  precipitation  than  upon  those  determining  solution.* 
Prof.  Posepny  points  out  more  than  once,  that  the  two  great  factors 
which  increase  the  solubility  of  all  substances  are  heat  and  pressure. 
We  know  by  observation  that  these  conditions  are  increasingly  ob- 
tainable as  we  go  downward.  The  deep  region  is  one  that  favors 
solution,  just  as  the  shallow  zone,  because  it  is  characterized  by  les- 
sened heat  and  diminished  pressure,  favors  precipitation.  It  is  this 
simple  fact  which  helps  to  explain  the  ordinary  non-persistence  of 
ore  in  depth.  It  is  this  which  explains  the  comparatively  late  origin 
of  ore-deposits.  The  general  non-persistence  of  ore  in  depth  is  a  fact 
capable  of  proof,  the  comparatively  late  origin  of  most  ore-deposits 
is  a  hypothesis  which  is  founded  upon  observation  and  confirmed  by 
the  consideration  that  the  older  geological  formations  were  at  some 
time  overlaid  by  an  enormous  thickness  of  later  sediments  and  there- 
fore existed  under  conditions  favoring  solution,  and  not  that  precipi- 
tation to  which  ore-deposition  is  more  directly  due. 

One  more  point  I  would  wish  to  refer  to.  Prof.  Posepny  demon- 
strates that  at  Przibram  the  metal  of  the  ore-deposits  could  not  have 
come  from  the  eruptive  rock  in  the  immediate  vicinity  of  the  lodes. 
This  is  most  interesting.  For  many  years  we  have  been  accustomed 
to  references  to  dikes  and  other  bodies  of  eruptive  rocks  as  being 
the  source  of  the  precious  metals  of  certain  lode-formations.  In  fact, 
a  "dike  "  was  almost  as  necessary  as  a  "true  fissure-vein/'  a  good 
climate,  plenty  of  timber,  fine  scenery  and  other  factors,  which,  in  a 
prospectus,  are  requisite  to  the  making  of  a  good  mine.  In  my  Beii- 
digo  paperf  I  have  already  suggested  that  the  vicinity  of  eruptive 
rocks  need  not  necessarily  indicate  that  they  were  the  source  of  the 
metals  but  that  their  extrusion  afforded  the  heat  which  made  the  un- 
derground waters  active.  I  would  add  that  the  contraction,  due  to 
cooling,  following  the  extrusion  of  a  sheet  or  a  mass  of  igneous  rock 


*  Reference  is  intended  particularly  to  the  metals.  f  Trans.,  xxii.,  289. 

12 


178  THE   GENESIS   OF   ORE-DEPOSITS. 

may  have  afforded  a  line  of  least  resistance  or — as  Prof.  Posepny 
would  put  it — "a  line  of  maximum  circulation." 

In  closing  I  would  express  the  indebtedness  which  we  must  all 
feel  to  Prof.  Posepny  for  so  extensive  and  so  valuable  a  contribution. 
In  my  own  case  I  would  express  it  as  the  gratitude  of  an  apprentice 
to  a  master. 

HORACE  Y.  WINCHEL.L,  Minneapolis,  Minn,  (communication  to 
the  Secretary)  :  It  is  an  interest  ing  fact  that  the  opinions  here  so  ably 
advanced  by  Prof.  Posepny  were  partially  stated  as  long  ago  as  the 
end  of  the  seventeenth  century.  A  few  quotations  from  "  An  Essay 
towards  a  Natural  History  of  the  Earth,"  by  John  Woodward,  will 
make  this  plain.  I  quote  from  the  third  edition,  published  in  1723, 
the  date  of  the  first  edition  being  1695. 

"  That  there  is  a  perpetual  and  incessant  circulation  of  water  in  the  atmosphere  ; 
it  arising  from  the  globe  in  the  form  of  vapour,  and  falling  down  again  in  the  form 
of  rain,  dew,  hail  and  snow.  That  the  quantity  of  water  thus  rising. and  falling  is 
equal ;  as  much  returning  back  in  rain,  etc.,  to  the  whole  terraqueous  globe,  as  was 
exhaled  from  its  vapours.  That  tho'  the  quantity  of  water  thus  rising  and  falling 
be  certain  and  constant  as  to  the  whole,  yet  it  varies  in  the  several  parts  of  the 
globe;  by  reason  that  the  vapours  float  in  the  atmosphere,  sailing  in  clouds  from 
place  to  place,  and  are  not  restored  down  again  in  a  perpendicular  upon  the  same 
precise  tract  of  land,  or  sea,  or  both  together,  from  which  originaly  they  arose,  but 
any  other  indifferently  "  (pp.  132,  133). 

As  to  the  cause  of  the  circulation  of  waters  beneath  the  surface  of 
the  earth  he  speaks  as  follows  : 

"That  there  is  a  nearly  uniform  fire  or  heat  disseminated  throughout  the  body  of 
the  earth,  and  especially  the  interior  parts  of  it ;  the  bottoms  of  the  deeper  mines 
being  very  sultry  and  the  stone  and  ores  there  very  sensibly  hot,  even  in  winter, 
and  the  colder  seasons.  That  'tis  this  heat  which  evaporates  and  elevates  the  water 
of  the  Abyss,  buoying  it  up  indifferently  on  every  side,  and  towards  all  parts  of  the 
surface  of  the  globe ;  pervading  not  only  the  fissures  and  intervalls  of  the  strata, 
but  the  very  bodyes  of  the  strata  themselves,  permeating  the  interstices  of  the  sand, 
earth  or  other  matter  whereof  they  consist,  yea  even  the  most  firm  and  dense  mar- 
ble and  sandstone.  .  .  .  That  this  vapour  proceeds  up  directly  towards  the  sur- 
face of  the  globe  on  all  sides,  and  as  near  as  possible,  in  right  lines,  unless  impeded 
and  diverted  by  the  interposition  of  strata  of  marble,  the  denser  sort  of  stone,  or 
other  like  matter,  which  is  so  close  and  compact  that  it  can  admit  it  only  in  smaller 
quantity,  and  this  very  slowly  and  leisurely. 

"That  where  the  vapour  is  thus  intercepted  in  its  passage,  and  cannot  penetrate 
the  stratum  diametricaly,  some  of  it  glides  along  the  lower  surface  of  it,  permeating 
the  horizontal  intervall  which  is  betwixt  the  said  dense  stratum  and  that  which  lies 
underneath  it.  The  rest  passes  the  interstices  of  the  mass  of  the  subjacent  strata, 
whether  they  be  of  laxer  stone,  or  of  marie,  or  the  like,  with  a  direction  parallel 
to  the  site  of  those  strata,  'till  it  arrives  at  their  perpendicular  intervalls  "  (pp.  136, 
137). 


THE   GENESIS   OF   ORE-DEPOSITS.  179 

Woodward  entertained  the  idea  that  "  the  whole  terrestrial  globe 
was  taken  all  to  pieces  and  dissolved  at  the  deluge," 

"  That  at  length  all  this  metallick  and  mineral  matter,  both  that  which  continued 
asunder,  and  in  single  corpuscles,  and  that  which  was  amassed  and  concreted  into 
nodules,  subsided  down  to  the  bottom  ;  at  the  same  time  that  did  the  shells,  teeth, 
and  other  like  bodyes :  as  also  the  sand,  cole,  marie,  and  other  matter  whereof  the 
strata  of  sand-stone,  cole,  marie,  and  the  rest  are  for  the  most  part  composed  ;  and 
so  were  included  in,  and  lodged  amongst,  that  matter.  .  .  .  And  the  case  of 
rnetalls  and  minerals  being  the  same,  'tis  for  that  reason  that  in  some  places  we  now 
get  iron,  or  vitriol,  but  no  copper  or  alum :  in  others  we  find  these,  but  not  those  : 
and  in  others  both  these  and  those,  and  perhaps  many  more.  .  .  .  Thus  we 
sometimes  see  whole  strata  compiled  of  metallick  and  mineral  nodules  :  others  of 
pebles,  and  of  flints,  without  the  interposition  of  other  matter.  .  .  .  Thus  like- 
wise we  find  strata  consisting  almost  entirely  of  common  salt:  others  of  ochre  :  and 
others  of  several  metalls  and  minerals,  tin,  lead,  vitriol,  nitre,  and  sulphur  promis- 
cuously, without  any  considerable  mixture  of  coarser  terrestrial  matter." 

Of  the  origin  of  veins  he  speaks  in  these  words  : 

"That  the  metallick  and  mineral  matter,  which  is  now  found  in  the  perpendicular 
intervalls  of  the  strata,  was  all  of  it  originaly,  and  at  the  time  of  the  deluge,  lodged 
in  the  bodyes  of  those  strata ;  being  interspersed  or  scatter'd  in  single  corpuscles, 
amongst  the  sand,  or  other  matter  whereof  the  said  strata  mainly  consist.  That  it 
was  educed  thence  and  transmitted  into  these  intervalls,  since  that  time;  the  intervalls 
themselves  not  existing  till  after  the  strata  were  formed,  and  the  metallick  and  min- 
eral matter  was  actualy  lodged  in  them ;  they  being  only  breaches  of  the  strata,  and 
not  made  till  the  very  conclusion  of  the  catastrophe,  the  water  thereupon  immedi- 
ately withdrawing  again  from  off  the  earth. 

"That  the  water,  which  ascends  up  out  of  the  Abyss,  on  all  sides  of  the  globe,  to- 
wards the  surface  of  the  earth,  incessantly  pervading  the  pores  of  the  strata,  I  mean 
the  interstices  of  the  sand  or  other  matter  whereof  they  consist,  detaches  and  bears 
along  with  it  all  such  metallick,  mineral,  and  other  corpuscles  which  lye  loose  in 
its  way,  and  are  withal  so  small  as  to  be  able  to  pass  those  interstices ;  forcing  them 
along  with  it  into  the  perpendicular  intervalls ;  to  which  it  naturally  directs  its 
course,  as  finding  there  a  ready  exit  and  discharge,  being  partly  exhaled  thence  up 
into  the  atmosphere,  and  partly  flowing  forth  upon  the  surface  of  the  earth,  and 
forming  springs  and  rivers. 

"That  the  water  which  falls  upon  the  surface  of  the  earth  in  rain,  bears  also 
some,  tho'  a  lesser,  share  in  this  action  ;  this,  soaking  into  the  strata  which  lye  near 
the  surface,  straining  through  the  pores  of  them,  and  advancing  on  towards  their 
perpendicular  intervalls,  bears  thither  along  with  it  all  such  moveable  matter  as 
occurs  in  those  pores  in  much  the  same  manner  as  does  the  water  which  arises  out 
of  the  Abyss  with  only  this  difference,  that  this  passes  and  pervades  none  but  the 
superficial  and  uppermost  strata,  whereas  the  other  permeates  also  those  which  lye 
lower  and  deeper.  (The  vadose  and  deep  underground  circulations  of  Posepny.}  .  .  . 

"  That  therefore  the  metalls  and  minerals  which  are  lodged  in  the  perpendicular 
intervalls  of  the  strata  do  still  grow  [to  speak  in  the  mineralogists'  phrase],  or  re- 
ceive additional  increase  from  the  corpuscles  which  are  yet  daily  borne  along  with 
the  water  into  them.  Nay  they  have  grown  in  like  manner  ever  since  the  time  of 


180  THE   GENESIS   OF   ORE-DEPOSITS. 

the  Deluge,  in  all  such  places  where  those  intervulls  are  not  already  so  filled  that 
they  cannot  receive  any  more :  or  where  the  stock  of  metallick  and  mineral  cor- 
puscles, originally  lodged  in  the  strata,  is  not  quite  exhausted,  and  all  borne  thither 
already.  .  .  . 

"That  the  metallick  and  mineral  matter  which  lyes  in  the  bodyes  of  the  strata 
does  not  grow,  .  .  .  but  on  the  contrary,  hath  been  diminished  and  lessened 
by  so  much  as  hath  been  conveyed  into  their  perpendicular  intervalls,  and  as  hath 
been  brought  forth  upon  the  surface  of  the  earth  by  springs,  rivers,  and  exhalations 
from  the  Abyss,  since  that  time.  That  notwithstanding  there  have  and  do  still 
happen,  transitions  and  removes  of  it,  in  the  solid  strata,  from  one  part  of  the  same 
stratum  to  another  part  of  it,  occasion'd  by  the  motion  of  the  vapour  towards  the  per- 
pendicular intervalls  of  these:  and  in  the  laxer  strata,  such  as  sand,  clay,  and  the 
like,/rom  the  lower  ones  to  those  which  lye  above  them,  and  even  to  the  very  surface  of 
the  earth  "  (pp.  208-216). 

Although  the  paragraphs  quoted  lead  us  to  infer  that  Woodward 
thought  veins  were  filled  by  the  mechanical  transportation  of  matter 
in  small  grains,  yet  there  are  in  other  places  indications  that  he  also 
had  an  idea  of  their  formation  by  the  deposition  of  minerals  from 
solution.  Thus,  nearly  a  century  before  Werner  and  Hutton,  were 
expressed  ideas  which  were  the  results  of  long  and  careful  observa- 
tion and  study  which,  though  tinged  with  the  theological  and 
so-called  philosophical  doctrines  of  the  day,  were  yet  true  to  nature 
and  of  universal  application,  and  which  strike  us  as  extremely  valu- 
able and  original  when  put  in  modern  logic  and  phraseology. 

JOHN  A.  CHURCH,  New  York  City  (communication  to  the  Sec- 
retary) :  I  cannot  agree  with  all  the  dicta  of  Prof.  Posepny's  valu- 
able paper.  He  says  (page  13,  and  see  page  68)  that  in  fissures 
"  only  the  places  remaining  open  would  permit  an  active  circulation 
of  solutions  and  a  regular  deposition  from  them."  The  idea  of 
deposition  in  a  free  space  runs  through  the  whole  of  the  paper  and  is 
applied  not  only  to  the  ore-deposits  of  the  vadose  circulation  but 
with  equal  uniformity  to  those  of  the  deep  circulation.  Such  ideas 
seem  to  me  to  be  incompatible  with  the  crushing  pressure  which  all 
agree  must  be  found  at  depths  of  10,000  and  15,000  feet.  We  have 
in  metasomatic  replacement  an  explanation  of  ore-formation  which 
accords  so  well  with  the  conditions  supposable  at  great  depth  that  it 
seems  unnecessary  to  add  to  it  a  requirement  that  is  certainly  con- 
tradicted by  those  conditions. 

I  believe  I  was  the  first  in  this  country  to  ascribe  the  formation 
of  an  important  vein  (the  Comstock)  to  metasomatic  alteration, 
which  I  then  called  "substitution,"  the  term  metasomasis  being 
suggested  in  the  same  year.  The  character  of  the  Comstock  ore  for- 
bids the  supposition  of  deposition  in  an  open  space ;  for  it  is  not 


THE   GENESIS  OF  ORE-DEPOSITS.  181 

quartz  but  a  mixture  of  quartz  and  fragments  of  the  wall-rock.  In 
the  opinion  of  experienced  men  more  than  half  of  the  rich  ore  mined 
from  the  heart  of  the  great  ore-bodies  was  "  porphyry,"  and  at  least 
the  proportion  was  great.  My  conclusion  was  disputed  by  Mr. 
Becker;  but  one  of  the  surest  advances  which  vein-geology  has 
made  in  the  last  fifteen  years  has  been  the  steady  growth  of  the  idea 
that  the  thickest  ore-bodies  may  have  been  formed  by  the  replace- 
ment of  masses  of  wall-rock  fragments,  or  by  the  spread  of  siliceous 
replacement  from  a  narrow  crevice  through  the  walls. 

In  deep-seated  formations  this  method  of  deposition  is  necessarily 
supposed  ;  for  there  are  not  only  no  open  spaces  there,  but  the  situa- 
tion is  not  even  what  I  conceived  it  to  have  been  in  the  Comstock. 
Nearer  the  surface  there  might  be  partings  which,  though  minute, 
would  be  real  openings,  while  at  great  depth  such  partings  must  be 
so  closely  appressed  as  to  be  no  more  than  mere  breaks  of  continuity. 

The  tendency  of  opinion  in  this  country  is  toward  metasomasis 
acting  upon  masses  of  crushed  rock  in  crevices  which  they  com- 
pletely fill ;  and  I  find  nothing  in  Prof.  Posepny's  paper  which 
need  cause  a  retreat  from  this  view. 

Prof.  Posepny  appears  to  place  great  reliance  upon  the  appearance 
of  the  ore  and  the  walls  enclosing  it  and  I  suppose  it  is  because  deep 
seated  deposits  in  limestone  have  some  strong  resemblances  to  those 
of  the  upper  circulation,  that  he  concludes  that  the  former  must  be 
laid  down  in  "  spaces  of  dissolution,"  like  some  of  the  latter.  To 
me  these  facts  point  rather  to  an  identity  of  active  agent  than  to 
identical  circumstances  of  its  action.  To  make  my  meaning  clearer 
I  will  recall  some  well-known  facts  and  theories. 

We  know  that  the  limestone  rocks,  in  proportion  to  their  amount, 
carry  more  ore- bodies  than  the  siliceous  rocks,  though  the  latter 
have  actually  the  greater  number.  The  suitability  of  limestone  for 
the  deposit  of  ores  is  usually  made  to  depend  upon  its  solubility  in 
water  charged  with  carbonic  acid,  which  is  supposed  to  be  derived 
from  the  soil  by  descending  waters.  It  is  carried  into  the  interior  of 
the  earth  and  again  discharged,  for  the  earth  being  a  closed  vessel 
already  full  of  water  into  which  a  new  supply  is  constantly  poured, 
it  is  clear  that  as  much  must  be  discharged  into  the  atmosphere  by 
springs  as  the  atmosphere  supplies  by  rain.  I  find  fault  with  the 
usual  view  upon  this  subject,  which  apparently  assumes  that  the 
deep  waters  must  be  highly  charged  with  CO2  derived  from  the  sur- 
face. On  the  contrary  it  seems  to  me  that  the  discharging  water  must 
bring  out  as  much  CO2  as  it  takes  in,  for  neither  water  nor  gas  can 


182  ,     THE   GKNESIH   OF   <  >K  K-DKI'nSITS. 

be  lessened  in  quantity  except  by  the  comparal  ivcly  small  amount 
tluitcntcrH  into  fixed  combinations  in  the  rocks.  Sinee  (lie  solubility 
of  gas  in  water  is  increased  by  pressure  we  must  suppose  (hat  the 
dissolved  CO2  remains  with  the  water  that  absorbed  it  throughout 
the  whole  range  of  cireulat ion  and  that  there,  cannot  be  any  discharge; 
of  surface  CO.,  in  the  interior.  Yet  we  know  that,  large  <|uantities 
of  CO..  an-  discharged  from  the  earth  as  gas  not  dissolved  in  water, 
besides  that  which  is  dissolved;  and  this  gaseous  discharge  must  be  in 
excess  of  the  (  '<  >,  carried  in.  May  we  not  find  the  source  of  (his 
excess  in  deep-seated  metasomatio  replacement? 

The  operation  of  solutions  whose  composition  we  do  not  know  can 
be  judged  only  by  their  effects.  When  metasomatie  replacement 
takes  place  in  limestone  it  is  generally  assumed  that  lime  carbonate 
goes  into  solution,  while  its  place  is  taken  by  the  ore-substances, 
that  is  to  say,  that  the  action  is  molecular  substitution  and  not 
atomic;  but  it  is  conceivable  that  the  change  should  begin  by  an 
interchange  of  acidic  elements — that  8i()2  should  drive  out  CO,. 
Subsequent  changes  might  remove  the  lime  silicate  by  another 
process  of  substitution,  since  it  is  more  soluble  than  silica  ;  but  the 
point  is  that  CO.,  would  be  liberated,  and  though  the  original  ore- 
solution  were  free  from  CO2,  it  would  immediately  become  charged 
with  that  agent  and  exert  the  well-known  dissolving  power  of  car 
bonic  acid  solutions.  In  this  way  a  solution  which  would  have  but 
feeble  power  in  oilier  rocks  may  in  limestone  set  up  a  chain  of  re- 
actions that  would  intensify  its  effects.  These  considerations  lead 
to  interesting  conclusions. 

We  have  a  source  of  CO2  in  rocks,  however  deep-sealed,  and  con- 
sequently effects  may  be  produced  at  any  depth,  which  simulate 
those  of  surface-waters,  though  probably  without  the  production  of 
caverns.  Since  the  mode  of  solution  is  the  same,  the  appearance  of 
the  walls  lining  an  ore-body  and  the  appearance  of  the  ore  itself 
may  be  almost  precisely  the  same  as  in  (he  vadose  region. 

Limestone  contains  the  elements  for  self-destruction,  since  the 
breaking  up  of  one  lime-carbonate  molecule  may  cause  (he  solution 
of  another;  and,  as  this  cannot  be  said  of  any  other  rock,  we  reach 
a  possible  explanation  of  the  comparative  frequency  of  ore-bodies  in 
limestone.  The  dolomites  would,  of  course,  present  similar  reac- 
tions. 

There  are  two  questions  which  are  distinguished,  even  in  the 
difficult  study  of  veins,  by  the  obscurity  which  hangs  over  them. 
One  is  the  selection  of  a  favored  stratum  for  ore-deposition.  In 


TIIK    (JHNKSIH    <>!«'    OIM'MJUPOHITH.  183 

some  situations  the  solutions,  before  readmit;    the  stratum  of  actual 
ore-deposition,   must    have    passed   several   strata    suitable    (or   their 
action,  if  they  had  possessed  from  the  beginning  the  power  of  solu- 
tion which    they  sliowe<l   ultimately.      I    believe   Iliis   objection    has 
been  urged  against  the  lateral-secretion    theory  unapplied    to    Lead 
ville.      ( )re-sol ill  ions  exhibit  a  selective  power  which  is  e\l  raordinary 
in  a  waler   fully   supplied    willi    dissolving    <pialilies,  but    <|iiitc    e\ 
plieable  in  a  solution  wliieli  lacks   (his    power.      I  suppose    it  IH  im- 
possible at   present  to  determine  why  (he  rocks  now  exposed  at  I  >ead- 
ville  were  selected  lor  altaek    by    (he  solutions;   but    I    think    it    is 
Comprehensible  why  that  aclion,  however  extensive,  should  be  local 
i/ed    by  the    development    and    aetion    of  CO2   in    the  neighborhood 
where  it  began. 

An  obvious  consequence  of  these  eonsiderations  is  that  the 
acpieous  circulation  of  (he  earth  becomes,  through  (he  medium  <>(' 
metasomasis,  a  means  Ibr  restoring  to  the  atmosphere  aecumulationH 
of  carbon  that  represent  (he  organic,  life  of  past,  times. 

The  seeond  obscure  (piestiou  is  logically  one  which  ought  to  be 
answered  before  wo  discuss  the  origin  of  ores  at  all.  It  iw  the  860- 
Ondary alteration  of  already-formed  ore-deposits.  1  have  no  doubt 
that  some  of  the  (top-seated  deposits  which  wo  see  are  actually  a 
product  of  the  vadose  circulation.  formed  ten  thousand  feet 
below,  they  have  been  raised  until  they  arc  now  ten  thousand  feet 
above  the  sea-level,  and,  during  the  immense  period  through  which 
they  have  been  subjected  to  the  surface  circulation,  they  have  not 
only  been  re  arranged  but  may  have  actually  lost  their  ancient 
origin.  Kvcn  tin;  rock  in  which  they  were  deposited  may  have  been 
removed  and  the  ore  transferred  to  another  member  of  the  series. 
Structural  facts  may  prove  deep-seated  deposition,  but  actually  the 
ore-bodies  we  see  are  often  in  whole  or  in  part  hysteromorpliH.  This 
is  especially  true  in  limestone  deposits.  Though  those  facts  are 
well-known,  they  do  not  exert  the  controlling  influence  upon  opinion 
which  I  think  they  deserve,  probably  because  of  the  extreme  diffi- 
culty of  separating  the  primary  from  the  secondary  phenomena.  No 
writer  that  I  have  seen  has  given  to  this  subject  half  the  importance 
which  a  mining  engineer  must  give  it. 

1  cannot  agree  with  the  author  in  giving  so  much  importance  to 
crustification,  as  IK;  describes  it.  Certainly  a  handed  structure  can 
arise  from  the  replacement  of  fragments'  arranged  in  layers  by  pres- 
sure and  friction,  as  well  as  in  many  other  ways,  and  does  not  prove 
deposition  in  a  cavity,  whether  filled  by  water  or  air.  He  has  mis- 


184  THE   GENESIS   OF   ORE-DEPOSITS. 

understood  me  in  saying  that  I  found  crusts  of  quartz  alternating 
with  calcite  in  the  Justice  mine  (Comstock).  I  said  the  thick  masses 
of  calcite  in  that  mine  rested  on  a  thin  layer — an  inch  or  two — of 
quartz;  but  this  is  not  crustification  in  the  author's  sense.  My 
view  of  that  occurrence  was  that  an  insignificant  quartz  seam,  prob- 
ably belonging  to  the  last  period  of  the  Comstock,  was  first  produced, 
and  that  the  calcite  was  formed  by  replacement  of  the  wall-rock  at 
a  later  period.  There  is  not  the  least  evidence  of  deposition  in  a 
cavity.  If  there  is  crustification,  that  appearance  does  not  have  the 
significance  which  our  author  gives  to  it. 

I  have  not  attempted  to  particularize  the  many  points  in  which 
I  find  myself  in  agreement  with  the  author;  and  since  my  remarks 
have  been  rather  in  criticism,  I  desire  to  express  in  conclusion  my 
high  appreciation  of  his  admirable  treatise. 

S.  F.  EMMONS,  Washington,  D.  C.  (communication  to  the  Secre- 
tary) :  Prof.  Posepny's  paper,  or  treatise,  as  it  rather  deserves  to  be 
called,  is  a  most  important  contribution  to  the  theory  of  ore-deposits. 
His  wide  personal  observation  of  most  of  the  important  mines  in  so 
many  different  parts  of  the  world  and  his  critical  acumen  as  an 
observer,  combined  with  his  long  continued  studies  of  the  subject, 
give  to  his  words  an  exceptional  authority.  Whatever  might  be 
said,  therefore,  in  praise  of  his  article  (and  it  would  take  much  time 
to  say  it  all)  would  hardly  add  to  its  value.  But  the  very  high 
quality  of  his  work  renders  any  errors  in  it  exceptionally  hurtful, 
and  I  shall  therefore  confine  my  remarks  mainly  to  what  seem  to  me 
to  be  erroneous  teachings,  and  to  points  in  which  I  differ  with  him 
either  wholly  or  in  part.  I  would  first  say,  however,  that  to  the 
greater  part  of  the  views  put  forth  in  this  paper  I  most  heartily 
subscribe,  especially  to  those  on  underground  circulation,  and  on  the 
great  rarity  of  ore-deposits  which  have  been  formed  contemporane- 
ously with  the  enclosing  rocks. 

It  is  well  known  that  for  some  years  past  there  has  been  a  very 
warm  discussion  between  Posepny  and  Stelzner  on  the  one  side,  and 
Sandberger  on  the  other,  in  regard  to  the  derivation  of  the  material 
of  ore-deposits,  the  former  holding  to  the  ascension,  the  latter  to  the 
lateral-secretion  theory.  Without  attempting  to  determine  the  merits 
of  either  side  of  the  controversy,  which  it  would  be  unwise  to  do 
without  examining  personally  the  deposits  in  question  and  their 
geological  surrounding,  one  is  inclined  to  believe  that  the  views  of 
either  of  such  able  geologists  must  have  scientific  value,  whether  one 
or  the  other  may  be  proved  to  be  erroneous  in  a  particular  instance. 


THE   GENESIS   OF   ORE-DEPOSITS.  185 

I  regret,  however,  to  see  this  controversy  brought  into  what  should 
be  a  broad  and  impartial  discussion  of  the  facts  of  nature,  and  to 
detect  in  certain  cases  what  appears  to  be  a  tendency  on  the  part  of 
Prof.  Posepny  to  adopt  a  rather  forced  construction  of  these  facts, 
in  order  to  make  them  support  his  views  rather  than  those  of  Sand- 
berger. 

The  lateral -secretion  theory,  which  Posepny  ascribes  to  Sandberger, 
is  much  narrower  than  that  which  T,  and  I  think  most  American 
geologists,  hold.  It  confines  the  derivation  of  the  vein-contents  to 
the  wall-rock  in  immediate  contact  with  the  deposit;  whereas,  in 
my  view,  a  derivation  from  rocks  within  reasonable  proximity,  as 
opposed  to  a  source  at  unknown  depths  ("in  the  barysphere "), 
would  constitute  lateral-secretion,  and  ore-bearing  currents  may  in 
such  cases  have  had  an  upward,  downward,  or  lateral  motion  accord- 
ing to  differing  local  conditions  of  rock-structure.  Prof.  Posepny 
himself  admits,  in  his  admirable  discussion  of  vadose  or  shallow  and 
deep  underground  circulation,  the  possibilities  of  such  lateral-secre- 
tion when  he  describes  the  latter  (p.  26)  in  the  following  words : 

"The  ground-water  descends  in  the  deep  regions  also  through  the  capillaries  of 
the  rocks ;  at  a  certain  depth  it  probably  moves  laterally  towards  open  conduits, 
and  reaching  these,  it  ascends  through  them  to  the  surface."  »: 

The  distinction  between  the  action  of  surface  and  that  of  deep- 
seated  waters  is  an  important  one  in  the  study  of  ore-deposition  ; 
but  I  do  not  think  that  Prof.  Posepny  is  justified  in  assuming,  as  he 
does,  that  only  ascending  waters  are  capable  of  depositing  ores. 
Futhermore,  the  necessary  derivation  of  metallic  minerals  by  these 
ascending  waters  from  the  "  barysphere'7  seems  too  far-fetched.  At 
what  depth  the  barysphere  will  be  found,  meaning  thereby  the  part 
of  the  earth's  interior  where  the  rocks  have  a  much  higher  specific 
gravity  than  those  that  come  under  our  observation,  is  purely  a 
speculative  question  ;  but  as  our  surface  observations  extend  over  a 
thickness  in  round  numbers  of  about  100,000  feet  of  rocks,  and  show 
no  appreciable  difference  of  specific  gravity  between  the  deeper  and 
more  shallow  rocks,  except  such  as  is  due  rather  to  different  degrees 
of  density  than  to  heavier  mineral  constituents,  it  seems  safe  to 
assume  that  such  a  barysphere  must  exist,  if  at  all,  at  such  great 
depths  as  to  be  beyond  the  reach  of  any  mineral-bearing  waters.  If 
such  a  zone  rich  in  heavy  metals  exists  in  depth,  as  there  is  some 
reason  to  believe,  my  own  view,  as  expressed  in  my  paper  read  at 
this  meeting,  is  that  the  heavy  metals  which  constitute  the  ore- 


186  THE   GENESIS   OF   ORE-DEPOSITS. 

deposits  were  brought  up  from  it  into  the  outer  crust  of  the  earth 
by  the  various  eruptive  rocks,  and  were  partially  concentrated  in 
certain  parts  of  these  eruptive  rocks,  by  differentiation  during  the 
process  of  cooling.  In  this  view  I  agree  with  Vogt,  whom  Prof. 
Posepny  mentions  (p.  134)  in  a  somewhat  slighting  manner.  I  differ 
with  Vogt,  however,  in  that  I  consider  the  greater  part  of  our  ore- 
deposits,  all  certainly  that  have  come  under  my  limited  observation, 
to  be  due  to  further  concentration,  perhaps  many  times  repeated, 
both  chemical  and  mechanical  ;  and  I  am  entirely  at  one  with  Prof. 
Posepny  in  considering  their  final  concentration  into  their  present 
form  to  be  due  to  the, action  of  circulating  waters. 

Prof.  Posepny's  belief  in  the  capabilities  of  an  ascending  current 
of  heated  waters  or  thermal  springs  seems  to  me,  in  some  instances, 
as  exaggerated  and  unreasonable  as  his  rendering  makes  Sand- 
berger's  disbelief,  in  the  instances  he  cites.  .  He  quotes  a  single 
observation  by  Noggerath  in  1845  on  the  finding  of  vertical  channels 
in  limestone  8  to  35  inches  in  diameter,  near  Aachen,  which  are  sup- 
posed to  have  been  eaten  out  by  the  ascending  spring-waters,  and 
from  this  draws  the  wide-reaching  conclusion  that  ascending  waters 
may  actually  force  their  way  up  through  rock  masses  without  the 
necessity  of  pre-existing  cracks  or  channels.  Among  instances 
where  he  uses  this  explanation  to  account  for  the  formation  of  an 
ore-deposit  the  most  remarkable  is  that  of  Laurium  (p.  124)  where 
the  ore-deposits  as  shown  by  the  diagrammatic  section  (Fig.  87)  are 
funnel-shaped  bodies  extending  outward  from  the  contact  of  flat- 
lying  schists  into  subjacent  and  superjacent  limestones,  that  is  both 
upwards  and  downwards.  My  own  explanation  of  this  section, 
deduced  by  observations  in  limestone-deposits  in  this  country,  would 
be  that  the  ore-bearing  currents  circulating  along  the  contact-planes 
had  eaten  outward  into  the  more  soluble  rock,  upwards  from  the 
upper  contact,  and  downwards  from  the  lower  contact.  But  Prof. 
Posepny  explains  the  funnel-shape  of  the  ore-bodies  on  the  upper 
contact  as  produced  "by  the  pressure  of  the  ascending  solutions." 
The  lower  contact  he  offers  no  explanation  for,  but  says  "it  is 
perhaps  somewhat  ideally  sketched." 

It  is  unprofitable,  however,  to  discuss  deposits  which  neither  of  us 
have  seen  ;  for  nothing  is  so  liable  to  misconception  as  the  description 
of  ore-deposits  one  has  not  seen  by  a  person  with  whose  qualifications 
and  accuracy  of  observations  one  is  not  familiar.  This  is  shown  in 
Prof.  Posepny 's  remarks  upon  the  Leadville  deposits,  in  which  he 
concludes  that  I  must  acknowledge  that  my  views  in  regard  to  the 


THE   GENESIS   OF   ORE-DEPOSITS.  187 

downward  course  of  the  ore-bearing  solutions  were  incorrect,  because 
several  mining  engineers  have  shown  them  to  be  untenable.  It  does 
not  seem  to  occur  to  him  that  the  views  of  a  mining  engineer  (who 
is  not  necessarily  a  geologist)  based  upon  studies  of  a  single  mine  or 
set  of  mines  would  be  of  less  value  as  applied  to  such  theoretical 
questions  than  those  of  a  trained  geologist  who  had  made  a  study  of 
all  the  geological  conditions  and  mines  of  a  district.  Of  the  three 
articles  quoted  by  him,  that  of  Mr.  Freelund  offers  no  opinion  upon 
the  subject  in  question.  Both  this  and  Mr.  Rolker's  article  were 
written  before  my  monograph  was  published,  otherwise  Mr.  Rolker 
would  have  found  his  objections  on  these  points  foreseen  and  ac- 
counted for  there  (p.  490). 

In  the  summer  of  1890,  I  spent  nearly  two  months  at  Leadville 
studying  the  recent  developments  with  the  special  purpose  of  testing 
the  correctness  of  my  former  deductions,  and  Mr.  Blow  accompanied 
me  through  the  workings  of  North  Iron  Hill  with  which  he  is  so 
familiar.  While  I  naturally  found  many  details  of  geological 
structure  which  were  not,  and  coufd  not  have  been,  correctly  repre- 
sented on  the  underground  sections  accompanying  my  report,  I 
found  no  reason  to  change  my  views  of  the  manner  of  formation  of 
the  ore-deposits,  and  I  convinced  myself  (and  I  think  Mr.  Blow 
also)  that  his  objections  were  based  on  a  misapprehension  of  certain 
geological  phenomena.  It  were  too  long  to  give  here  all  the  results 
of  my  observations,  which  I  regret  that  circumstances  beyond  my 
control  have  as  yet  prevented  me  from  publishing.  I  will  say,  how- 
ever, as  bearing  upon  this  point,  that  in  no  case  did  I  find  any  con- 
vincing evidence  of  the  action  of  ascending  solutions.  The  ore- 
bodies  occur  in  two  general  forms,  either  on  the  approximately  hori- 
zontal contact-planes  of  porphyry  and  limestone,  or  along  nearly 
vertical  fissures  crossing  the  limestone  beds.  In  either  case,  wherever 
the  form  of  the  ore-body  was  such  as  to  throw  any  light  upon  the 
probable  direction  of  the  ore-forming  currents,  it  showed  that  they 
must  have  descended,  for  they  all  terminated  more  or  less  in  a  point 
or  wedged  out  downwards. 

Before  discussing  this  further,  it  may  be  well  to  repeat  my  state- 
ment given  in  the  monograph  (p.  379)  which  has  evidently  been 
overlooked  or  misapprehended  by  my  critics.  I  say,  with  regard  to 
the  immediate  source  of  the  ores  : 

"1.  That  they  came  from  above.  2.  That  they  were  derived  mainly  from  the 
neighboring  eruptive  rocks. 

"  By  these  statements  it  is  not  intended  to  deny  the  possibility  that  the  materials 


188  THE   GENESIS   OF   ORE-DEPOSITS. 

may  originally  have  come  from  great  depths,  nor  to  maintain  that  they  were  neces- 
sarily derived  entirely  from  eruptive  rocks  at  present  immediately  in  contact  with 
the  deposits." 

I  do  not  maintain,  as  many  have  assumed,  that  the  ore  was  derived 
from  the  white  porphyry.  I  do  not  pretend  to  be  able  to  determine 
what  particular  body  of  porphyry  it  came  from.  The  objection  of 
Mr.  Blow  that  it  could  not  have  come  from  the  white  porphyry  be- 
cause this  is  not  all  decomposed  (not,  "not  at  all  decomposed,"  as 
Prof.  Posepny  puts  it),  is  based  upon  a  misapprehension  of  what 
constitutes  decomposition.  If  Prof.  Posepny  will  read  the  descrip- 
tion of  the  eruptive  rocks  in  my  chapter  on  rock-formations,  he  will 
see  that  all  the  Leadville  porphyries  are  more  or  less  decomposed 
within  this  district;  when  Mr.  Cross  and  I  were  making  our  geo- 
logical studies  we  had  to  go  several  miles  away  before  we  could 
find  a  specimen  of  unaltered  white  porphyry  for  microscopical 
study. 

My  contention  with  regard  to  the  ores  of  this  district,  as  opposed 
to  the  theoretical  views  of  Prof?  Posepny  and  those  of  his  school, 
would  not  have  been  essentially  affected,  however,  if  it  had  been 
shown  that  the  solutions  had  ascended  to  reach  the  locus  of  the 
present  deposits.  The  fissures  across  the  limestone  which  gave  ac- 
cess to  the  solutions  forming  the  ore-shoots  of  North  Iron  Hill  de- 
scribed by  Mr.  Blow  are,  as  I  showed  in  my  monograph,  faults 
with  only  a  few  feet  of  displacement,  and  can  extend  to  only  limited 
depth ;  in  some  cases  their  lower  limit  could  be  detected.  The 
great  faults  which  extend  several  thousand  feet  in  depth  are  not  ore- 
bearing,  except  in  so  far  as  ore  has  been  dragged  into  them  in  the 
movement  of  their  walls,  one  upon  the  other.  But  the  extent  in  depth, 
even  of  these  great  faults,  must  be  extremely  limited  as  compared 
with  the  distance  of  the  barysphere.  I  believe  that  the  eruptive 
rocks  originally  brought  up  the  heavy  metals  from  the  depths  into 
the  general  region  in  which  the  ores  are  now  found.  Some  of  these 
eruptives  still  contain  over  four  per  cent,  of  them,  in  spite  of  all 
the  leaching  to  which  they  have  been  exposed.  The  ore-deposits 
are  concentrations  of  these  materials  by  deep  underground  waters, 
flowing  along  natural  channels,  and  depositing  along  those  which 
admitted  a  comparatively  free  flow,  as  compared  with  a  capillary 
circulation.  Such  a  flow  may  have  been  upward,  downward  or 
lateral,  according  to  varying  structural  conditions.  The  ascending 
solutions  which  Prof.  Posepny  contemplates,  however,  could  not 
have  formed  ore-bodies  of  the  form  of  those  found  in  Leadville;  and 


THE   GENESIS   OF   ORE-DEPOSITS.  189 

it  was  for  that  reason  that  I  laid  stress  upon  the  evidence  of  their 
probable  downward  course. 

As  regards  the  phenomena  of  "  crustification,"  I  may  not  have 
been  explicit  enough  in  stating  its  absence.  In  my  original  exam- 
ination I  searched  in  vain  for  any  evidence  of  it.  In  my  second 
examination,  almost  entirely  in  bodies  of  unaltered  sulphides,  I 
found  overwhelming  evidence  that  the  ore  was  not  deposited  in  pre- 
existing cavities,  but  by  metasomatic  replacement  of  the  limestone. 
In  the  great  bodies  of  the  A.  Y.,  Minnie  and  adjoining  mines  not 
only  could  every  detail  of  the  granular  structure,  joints  and  cleavage 
of  the  original  limestone  be  detected  at  times  in  the  sulphide  ore, 
but  even  the  cracks  in  the  top  of  the  ore-body  through  which  the 
ore- bearing  solutions  had  descended  were  often  visible.  In  aban- 
doned drifts,  where  the  limestone  dust  had  accumulated  on  the 
walls,  one  would  have  supposed  the  walls  to  be  all  limestone  until 
the  breaking  off  of  a  fresh  fragment  by  the  hammer  showed  the 
metallic  gleam  beneath. 

G.  F.  BECKER,  Washington,  D.  C.  (communication  to  the  Presi- 
dent from  Newport,  R.  I.) :  The  paper  of  Prof.  Posepny  is  a  very 
valuable  contribution  to  the  science  of  ore-deposits,  and  deserves  a 
more  careful  critical  discussion  than  I  am  able  to  assist  in  giving 
to  it  at  this  time,  in  the  absence  of  facilities  for  reference  to  au- 
thorities, etc.  A  few  general  observations,  therefore,  must  suffice 
at  present  to  indicate  my  views. 

The  theory  of  the  substitution  of  ore  for  rock  is  to  be  accepted 
only  when  there  is  definite  evidence  of  pseudomorphic,  molecular  re- 
placement. Prof.  Posepny  is  very  clear  on  this  point  (p.  12),  and 
I  have  insisted  upon  it  in  my  memoir  on  quicksilver-deposits  and  in 
a  paper  on  quicksilver  about  to  be  distributed.  Prof.  Posepny  ap- 
pears to  me,  on  the  other  hand,  to  lay  too  much  weight  upon  the 
structure  which  he  calls  "  crustification,"  as  indicating  exclusively 
the  filling  of  open  cavities  and  the  absence  of  replacement.  Meta- 
morphic  processes  are  very  frequently  accompanied  by  the  forma- 
tion of  layers  similar  to  stratification  and  crustification,  and,  indeed, 
from  similar  causes.  Strata  are  distinguishable  only  because  the 
circumstances  of  deposition  undergo  more  or  less  marked  variations, 
and  the  banded  structure  of  agate  or  hematite  is  also  due  to  varia- 
tions in  conditions  of  deposition  such  as  the  strength  of  the  solutions, 
or  the  rapidity  of  their  flow,  or  temporary  changes  in  the  composi- 
tion of  the  fluid.  It  appears  to  me  that  the  banded  structure  at- 
tending metamorphism,  as  a  matter  of  observation  in  many  cases, 


190  THE   GENESIS   OF   ORE-DEPOSITS. 

is  due  to  entirely  similar  causes.  Thus  a  mass  of  iron  immersed  in 
a  copper-solution  will  precipitate  the  copper  as  a  laminated  mass, 
unless  great  precautions  are  taken  to  secure  uniformity  of  tempera- 
ture, etc.  In  short,  lamination  is  an  ordinary  attendant  of  processes 
of  deposition,  whether  by  replacement  or  otherwise,  whenever  they 
are  so  slow  as  to  be  subject  to  changes  of  condition.  Hence  crusti- 
fication  seems  to  me  an  insufficient  guide  to  genetic  diagnosis. 

The  indications  of  replacement  which  I  should  rely  upon  are 
twofold  :  crystalline  pseudomorphosis  and  the  irregular  enlargement 
of  fissuies  in  the  replaced  mass.  Of  the  latter,  Prof.  Posepny  gives 
a  good  illustration  (Fig.  85).  As  for  pseudomorphosis,  it  has  a 
very  important  bearing  on  the  work  of  Mr.  Emmons  and  of  J.  S. 
Curtis,  for  it  appears  to  be  thoroughly  well  established  that  galena 
forms  pseudomorphs  after  calcite;  and,  therefore,  the  theory  of  re- 
placement of  limestone  which  they  advocate  is  to  say  the  least  possible. 
The  studies  of  these  observers  at  Lead vi lie  and  Eureka  tend  to 
show  that  replacement  has  been  the  chief  process;  but  so  far  as  I 
can  recall  their  remarks  they  do  not  assert  the  entire  absence  of 
deposition  in  pre-existing  openings;  so  that  even  if  crustification 
were  an  infallible  sign  of  filling,  the  detection  of  crusts  (Posepny, 
p.  104)  would  not  invalidate  their  position.  Another  objection  to 
Mr.  Emrnons's  views  is  expressed  by  Prof.  Posepny  in  the  sentence 
(p.  99),  "It  is  difficult  to  believe  that  metasomatic  processes  could 
produce  such  pronounced  ore-shoots  as  those  described  at  Leadville." 
I  cannot  share  this  view,  for  replacement,  like  solution,  must  occur 
along  fissures  or  channels,  and  metasomatic  ore-bodies  will  present 
analogies  in  form  to  the  open  spaces  of  caves  of  solution. 

It  seems  substantially  certain  that  open  cavities  in  limestones  can 
form  only  above  the  permanent  water-level  of  a  country,  since  in 
such  a  country  the  water  below  this -level  must  be  approximately 
saturated  with  calcium  carbonate.  On  the  other  hand,  replacement 
may  take  place  at  any  depth.  Now,  in  the  Great  Basin,  the  Ter- 
tiary and  Early  Quaternary  were  very  wet  periods,  and  if  the  Eu- 
reka limestones  have  been  excavated  by  surface  waters,  the  excava- 
tion and  subsequent  ore-deposition,  according  to  Prof.  Posepny's 
view,  must  be  crowded  into  the  late  Quaternary.  The  present  pre- 
cipitation of  that  region  would  seem  insufficient  to  bring  about  much 
cave  formation,  while  a  greater  precipitation  would  raise  the  water- 
level.  Thus,  so  far  as  Eureka  goes,  the  hypothesis  of  subsequent 
filling  raises  distinct,  though  perhaps  not  insuperable,  difficulties  as 
to  the  formation  of  the  cavities. 


THE   GENESIS   OF   ORE-DEPOSITS.  191 

The  foregoing  notes  should  be  reinforced  by  examples  and  cita- 
tions which  I  cannot  now  furnish. 

F.  M.  F.  CAZIN,  Hoboken,  N.  J.  :  If  I  venture  to  add  a  few 
lines  to  Prof.  F.  Posepny's  treatise  on  the  genesis  of  ore-deposits,  my 
justification  is  derived  from  practical  work  done  and  consequent 
opportunities  enjoyed  in  a  region,  to  which  the  learned  author  per- 
sonally has  remained  a  stranger,  and  of  which  in  existing  literature 
no  such  account  is  available,  as  would  afford  to  him  the  powerful 
argument  in  favor  of  his  theories  really  presented  by  the  region  it- 
self, to  a  degree  of  importance  beyond  any  other  mentioned  by  him. 

The  region  to  which  I  refer  furnishes  a  demonstration  of  the 
xenogenous  origin  of  ore-deposits,  heretofore  considered  as  idio- 
genous,  which  I  may  properly  call  gigantic,  and  which  is  equalled 
nowhere  on  the  face  of  the  earth,  as  far  as  known.  I  refer  to  the 
region  so  tersely  described  by  James  Douglas  (Trans.,  xix.,  694),  in 
these  words : 

"  In  the  Appalachian  chain  from  Vermont  to  Georgia,  there  are 
imbedded  in  the  crystalline  schists  large  masses  of  pyrites,  some  con- 
sisting of  ordinary  bisulphide  of  iron  but  most  of  them  of  pyrrho- 
tite,  and  all  carrying  more  or  less  copper." 

There  is,  on  the  long  stretch  from  Vermont  (Mr.  Douglas  might 
have  truly  said  "  from  Canada  and  Maine  ")  to  Georgia,  no  older 
mine,  and  none  with  more  important  development  on  the  ore- 
deposits  thus  described,  than  that  which  has  been  called  by  State- 
legislative  act  "  the  Vermont  Copper  Mine."  Its  history  began  be- 
fore the  world  knew  about  copper  on  the  shore  of  Lake  Superior. 
For  many  years  it  produced  at  the  rate  of  3,500,000  pounds  of  cop- 
per per  annum,  and,  with  adequate  improvements,  could  do  so  to- 
day. I  have  seen  its  developments  on  a  deposit  dipping  24°  N.E. 
to  a  distance  of  2350  feet  from  the  surface,  and  to  a  vertical  depth 
below  sea-level  of  several  hundred  feet,  the  lateral  expansion  of  stopes 
ranging  between  50  and  350  feet.  Having  been  connected  with  this 
mine  from  early  in  1882  to  June  of  1888,  I  have  had  opportunity 
to  search  for  the  origin  of  the  ore-body  there  exploited. 

Having  discovered  unmistakable  local  evidence  as  to  the  true  na- 
ture of  such  origin,  it  remained  to  ascertain  the  identity  or  uniform- 
ity of  effect  from  identical  causes  on  other  deposits  falling  under  the 
description  above  quoted  ;  and  it  was  not  difficult  to  establish  such 
identity  and  harmony. 

At  a  distance  of  ten  miles  in  a  northerly  direction  another  mine 
in  the  same  geological  position,  at  Corinth,  offered  evidence  leading 


192  THE   GENESIS   OF   ORE-DEPOSITS. 

to  the  same  conclusions,  and  in  a  southern  direction  at  a  distance  of 
four  miles,  the  Strafford  mines,  and  at  a  further  distance  of  sixteen 
miles  the  Pompanoosuc  mine,  all  similarly  situated,  demonstrated 
the  same  effects  under  similar  causes.  And  a  visit  to  many  other 
localities  within  the  Huronian  Appalachian  region  could  confirm 
only  the  conclusions,  to  which  the  observations  in  the  Vermont 
mine  had  been  leading  me. 

Except  as  to  dip,  topography  and  shape  of  workings,  Fig.  56  in 
Prof.  Posepny's  paper  might  well  serve  as  the  image  of  the  Ver- 
mont ore-deposit,  represented  on  a  vertical  plane  along  its  dip.  And 
Figs.  54  and  55  may  well  serve  as  a  representation  of  horizontal  and 
vertical  planes,  as  they  are  seen  inside  and  outside  of  the  Vermont, 
Corinth  and  Strafford  mines,  where  the  designs  shown  in  these  fig- 
ures not  only  occur  in  dimensions  varying  from  a  few  fathoms  to 
many  hundreds  of  fathoms,  but  also  in  varying  material.  In  the 
mine,  this  consists  of  the  sulphides  of  iron  and  copper,  and  outside 
and  at  distant  points  therefrom,  in  an  admixture  of  carbon-matter 
(graphite)  in  the  country-rock.  This  rock  is  a  micaceous  schist,  the 
graphitic  part  varying  in  proportion  from  a  mere  trace  to  100  per 
cent.,  becoming  marketable  plumbago  in  many  localities,  though 
without  sufficient  extent,  as  a  rule,  for  exploitation. 

But  it  is  not  on  the  similarity  of  design  between  sulphide  and  car- 
bon admixtures  in  the  rock  alone,  that  my  conclusions  were  built,  as 
a  description  of  the  mine  will  further  show. 

In  their  lateral  expansion  the  ore-stopes  in  the  Vermont  mine 
present  a  figure  very  similar  to  the  one  presented  in  Prof.  Posepny's 
Fig.  93,  if  the  longitudinal  extent  be  assumed  as  2350  feet,  with  the 
lower  part  broadened.  But  similar  figurations  are  also  presented  on 
a  smaller  scale,  where  in  quarries  the  rock  is  laid  bare  on  one  of  its 
dark  seams. 

The  roof  and  floor  of  the  Vermont  ore-deposits  are  virtually  im- 
penetrable to  water  ;  the  mine  at  1000  feet  vertical  depth  being  dry. 
But  there  is  uncovered  at  a  distance  of  a  few  hundred  feet  from  the 
outcrop  an  almost  vertical  cross-fissure  or  fault  (without  perceptible 
faulting),  filled  with  calcareous  spar  containing  sparsely  distributed 
small  seams  of  galena,  which  cross-fissure  allows  a  few  hundred  gal- 
lons of  water  a  day  to  percolate  into  the  workings.  Some  of  this 
water  finds  its  exit  through  an  abandoned  adit.  Where  it  reaches 
the  surface,  and  where  its  flow  is  slow,  allowing  evaporation,  it  de: 
posits  a  slime  of  virgin-white  carbonate  of  lime;  and  as  it  passes 
down  into  the  valley,  it  deposits  for  miles  a  mixture  of  carbonates  of 


THE   GENESIS   OF   ORE-DEPOSITS.  193 

lime  and  iron,  giving  to  the  creek-beds  their  peculiar  coating  of 
color,  as  a  result  of  atmospheric  reduction  of  the  iron  carbonate. 

The  ore  of  the  Vermont  in  its  mineral  character  has  one  main 
peculiarity,  which  is  common  to  the  deposits  as  described  from 
Canada  to  Virginia  and  Georgia,  namely,  that  quantitative  analysis 
shows  neither  the  figures  required  to  constitute  the  one  of  its  com- 
ponents as  ferro-sulphide,  nor  those  required  to  show  it  as  ferri-sul- 
phide,  these  figures  varying  all  the  way  between  those  applying  to 
FeS  and  those  applying  to  FeS2. 

The  structure  of  the  ore  is  the  same  as  that  of  the  graphitic  rock, 
with  the  same  variations  in  the  ore  as  to  contents  in  sulphides,  as 
there  are  in  the  country-rock  as  to  contents  in  carbon-matter.  That 
in  no  case  I  have  met  with  a  nucleus  of  carbon  in  a  body  of  sul- 
phides, I  have  attributed  to  a  full  completion  of  the  metamorphosis. 

Yet  another  feature  is  common  to  the  ores  of  the  described  de- 
posits. For  a  long  distance  on  the  northern  part  of  these  conti- 
nental deposits,  wherever  they  occur  in  the  Huronian  schists,  their 
ores  carry  nickel  in  proportions  varying  from  a  mere  trace  in  the 
copper- metal  made  therefrom  to  an  available  percentage  in  the  ore 
itself. 

Although  much  disinclined  to  draw  generalizing  conclusions  from 
isolated  geognostic  phenomena,  I  claim  justification  in  the  case  at 
hand  for  the  following  conclusions,  because  the  evidence  is  such  as 
repeats  itself  on  a  large  area,  and  once  understood  presses  itself 
upon  our  attention,  so  as  to  be  no  longer  ignored  : 

1.  The  iron   and  copper  sulphides  occurring   in  the  Huronian 
crystalline  schists  on  the  eastern  part  of  the   North  American  con- 
tinent have  locally  displaced  carbonaceous  matter,  where  faulting  of 
strata  aided  water-circulation,  such  water  containing  sulphate  salts 
of  the  metals  in  solution. 

2.  The  metamorphic  action  of  absorbing  mineral  carbon  and  of 
setting  free  CO2  is  continuous  to  the  present  day. 

3.  The  product  of  such  action   extending  below  sea-level   being 
observable  in  lines  nearly  parallel  with  the  coast-line  of  an  entire 
continent,  and  showing  equal  peculiarities  in  composition  on  the  en- 
tire line,  it  is  reasonable  to  assume  oceanic  action. 

It  is  true  that  the  ocean  of  our  period  evinces  the  presence  of 
copper  only  by  its  presence  in  maritime  organisms.  But  when,  on 
the  shores  of  a  once  existing  Triassic  sea  we  find  embedded  in  mas- 
sive but  porous  sand-rock  an  entire  palm- vegetation,  that  has  turned 
into  copper-glance,  as  my  eyes  have  seen  it  (compare  p.  120  of 

13 


194  THE   GENESIS   OF   ORE-DEPOSITS. 

Prof.  Posepny's  paper),  then  we  may  well  assume  the  presence  of  a 
perceptible  quantity  of  copper  in  a  Triassic  sea,  though  not  neces- 
sarily sufficient  to  destroy  animal  life.  It  is  even  a  matter  of  time 
only  for  an  ocean  like  the  one  of  our  own  period  to  provide  Pecil- 
lopora  and  Heteropora  corals  with  their  copper,  or  to  be  the  means 
of  metamorphosis  of  carbon-deposits  into  copper-sulphides  in  part; 
the  percentage  of  copper  in  these  deposits  being  in  general  not 
above  three  per  cent,  of  the  deposits  as  a  whole. 

I  find  a  further  justification  for  stating  these  facts  and  the  conclu- 
sions to  which  they  lead  in  the  circumstance,  that  the  learned  author, 
although  mentioning  the  occurrence  of  graphite  in  crystalline  schists, 
does  not  mention  that  this  graphite  anywhere  accounts  for  the  origin 
of  ore-beds. 

The  description  of  the  Sudbury  ore-beds  deals  with  a  case  far 
more  complicated  than  those  considered  by  me,  because  there  Hu- 
ronian  strata  similar  to  those  met  at  the  different  mines  in  the  Ap- 
palachians, have  been  disturbed  by  more  recent  dioritic  eruptions, 
which  subjected  the  pre-existing  ore-beds  to  a  new  partial  or  second 
metamorphosis,  by  which  the  true  state  of  affairs  is  very  materially 
obscured,  misleading  the  describers  into  the  untenable  assumptions, 
so  justly  controverted  by  the  learned  author.  Had  he  been  in- 
formed of  the  facts,  as  I  have  described  them  above,  the  author  of 
this  eminently  interesting  and  progressive  essay  on  the  genesis  of 
ore-deposits  would  have  been  able  to  knock  the  last  crutch  from 
under  the  theory  of  an  eruptive  origin  of  the  ore-deposits  at  Sud- 
bury and  elsewhere  in  the  crystalline  rocks  of  the  Huronian 
period. 

I  take  this  opportunity  to  furnish,  on  another  point,  information 
for  which  Prof.  Posepny  apparently  calls  (p.  121). 

A  few  months  only  after  my  report  on  the  Nacimiento  copper- 
occurrence  was  published,  with  the  consent  of  those  interested,  in 
the  Engineering  and  Mining  Journal,  Aug.  7  and  14, 1880,  the  United 
States  surveyors,  who  were  commissioned  by  the  Surveyor-General 
of  New  Mexico  to  survey  the  twenty-one  mining  claims  described 
by  me,  were  driven  off  these  claims  by  a  numerous  band  of  jumpers, 
who  had  swarmed  into  those  parts  as  the  usual  avant-garde,  indicat- 
ing, as  stormbirds  the  storm,  the  approach  of  a  new  railroad  line  in 
those  remote  parts.  To  reinstate  the  legitimate  owners  either  brutal 
force  or  litigation  had  to  be  employed.  The  ill-success  of  other 
copper- enterprises  in  New  Mexico,  though  quite  foreign  to  all  natu- 
ral conditions,  caused  them  to  resort  to  neither.  When,  in  1891,  I 


THE   GENESIS   OF   ORE-DEPOSITS.  195 

again  visited  the  upper  Rio  Grande  valley,  I  found  on  the  platform 
of  the  railroad-station  at  Bernalillo,  N.  M.,  about  a  car-load  of  the 
precise  cuprified  palm-vegetation  formerly  described  by  me,  showing 
that  there  had  survived  some  activity  at  Nacimiento  ;  but,  as  stated 
in  my  first  report,  profitable  operations  are  possible  only  on  a 
scale  like  that  on  which  lead  is  obtained  from  a  similar  sand-rock 
at  Mechernich  in  Rhenish  Prussia. 


DISCUSSION 

AT   THE  VIRGINIA   BEACH    MEETING,   FEBRUARY,   1894,   IN- 
CLUDING COMMUNICATIONS  SUBSEQUENTLY  RECEIVED. 

T.  A.  RICKARD,  Denver,  Colorado  (communication  to  the  Secre- 
tary) :  The  paper  of  Professor  Posepny  was  printed  so  short  a  time 
before  the  Chicago  meeting  that  it  could  not  receive  at  that  meeting 
the  thorough  discussion,  based  upon  careful  study,  which  its  great 
importance  and  value  deserved.  In  the  remarks  which  I  made  on 
that  occasion,  I  could  do  little  more  than  express,  with  others,  our 
thanks  to  the  distinguished  author  for  this  admirable  treatise  on  a 
subject  of  such  general  and  permanent  interest.  Further  examina- 
tion of  it  has  confirmed  the  opinion  that  its  appearance  marks  an 
epoch,  particularly  in  this  country,  in  the  study  of  ore-deposits,  and 
their  origin,  and  has  led  me  to  feel  that  our  appreciation  of  it  will 
be  best  expressed  in  aiding  its  purpose  and  widening  its  usefulness 
by  the  free  contribution  of  facts  and  interchange  of  views  which  it 
invites. 

I  have,  elsewhere,*  expressed  some  dissatisfaction  with  the  new 
names  introduced  in  this  paper;  and  it  has  seemed  to  me,  also,  that 
the  classification  of  ore-deposits,  which  it  proposes,  is  unnecessarily 
complicated.  From  the  stand-point  of  a  mining  engineer,  we  have 
had,  in  my  judgment,  no  classification  more  practical  and  sensible 
than  that  suggested  by  Dr.  Raymond,  twenty- five  years  ago  (outlined 
on  page  6  of  Professor  Posepny's  paper).  If  any  modification  of  it 
be  permissible,  I  would  suggest  the  following  : 

I.  Surface-Deposits. 

A.  Due  to  mechanical  agencies. 

B.  Due  to  chemical  agencies. 

*  Eng.  and  Min.  Jour. 


196  THE   GENESIS   OF   ORE-DEPOSITS. 

II.  Inclosed  Deposits. 

A.  Bedded. 

a.  Contemporaneous,  in  origin,  with  country-rock. 
6.  Subsequent,  in  origin,  to  country-rock. 

B.  Not  bedded. 

a.  Due  to  dislocation. 
6.  Due  to  impregnation. 

Surface-deposits  have  no  regular  form,  and  are,  therefore,  distin- 
guished primarily  by  their  origin.  Class  A  would  be  typified  by 
gold-bearing  placers,  and  Class  B  by  deposits  of  bog  iron-ores. 

When  we  come  to  inclosed  deposits,  we  find  an  extreme  com- 
plexity ;  but,  we  readily  recognize  that  some  are  conformable  to  the 
bedding  of  the  country-rock,  while  others  are  independent  of  it.  We 
can  further  distinguish  those  which  are  of  contemporaneous  origin, 
such  as  the  coal-beds,  from  those  which  were  formed  after  the  de- 
position of  the  country-rock.  To  this  class  belong  ore-deposits  which 
have  replaced  beds  of  limestone;  and  another  pretty  example  is 
afforded  by  the  Bendigo  saddle-reefs,  which  are  conformable  to  the 
anticlinal  curves  of  the  country-rock,  but  were  clearly  formed  after 
both  the  original  sedimentation  and  the  subsequent  folding. 

Among  the  non-bedded  deposits  there  is  no  limit  to  diversity  of 
structure  and  of  origin.  We  recognize,  however,  that  the  fissure- 
veins  which  cut  across  the  bedding,  but  retain  a  definite  position  due 
to  their  formation  along  lines  of  original  dislocation,  may  be  dis- 
tinguished from  the  irregular  impregnations,  due  as  much  to  the 
chemical  composition  of  the  country-rock  as  to  its  structure.  These 
two  types,  however,  are  forever  intermingled.  It  is  seldom,  indeed, 
that  an  ore-deposit  has  not  some  features,  however  faint,  of  form  and 
structure  dependent  upon  those  of  the  country-rock,  while,  on  the 
other  hand,  it  is  not  often  that  a  fissure- vein  is  found  which  does  not 
exhibit,  in  places,  a  lack  of  definition,  due  to  metamorphic  action 
upon  its  inclosing  walls. 

In  the  discussion  of  the  origin  of  fissures,  Prof.  Posepny  has 
touched  upon  a  point  which  has  been  the  subject  of  frequent  debate. 
I  fully  believe  that  dislocation  accompanies  the  formation  of  a  fis- 
sure, and  that  a  movement  of  its  walls  is  often  evidenced  by  slick- 
ensides  and  stria?.  Yet,  this  has  been  questioned  by  one  or  two 
members  of  the  Institute  who  are  known  to  be  both  accurate  and 
experienced  observers.  The  question  at  issue  is  a  vital  one,  if  we 
desire  to  obtain  a  clear  idea  of  the  mode  of  formation  of  mineral 


THE  GENESIS   OF  ORE-DEPOSITS.  197 

veins.  It  has  been  denied  that  the  striae  and  sl'ckensides  observed 
upon  the  walls  of  lodes  necessarily  prove  that  movement  has  taken 
place ;  but  it  has  never  been  clearly  shown  what  other  agency  did 
form  them.  Prof.  John  A.  Church  has  discussed  this  matter  in  a 
most  interesting  way,*  and  has  pointed  out  that  slickensides  may  be 
formed,  not  only  by  rubbing  but  also  by  "  deformation,  as  when  a 
plastic  substance  like  clay  is  forced  through  an  opening,"  and  again 
by  deposition  in  fine  parallel  lines.  Recently,  Prof.  Daubree  has 
experimentally  proved  that  gases  under  high  pressure  are  capable  of 
producing  striae  upon  rock-surfaces. f  It  is  true  that  a  distinction  is 
made  between  striae  and  slickensides,  but  I  look  upon  the  two  as  the 
work  of  the  same  agency.  In  the  former  case  we  have  coarse  rub- 
bing due  to  large  particles,  and  in  the  latter,  fine  polishing  due  to 
minute  particles.  There  is  no  doubt,  however,  that  certain  struc- 
tures are  called  striae,  which  are  to  be  ascribed  to  causes  other  than 
those  usually  supposed  to  produce  striae  and  slickensides.  As  I 
write  I  have  before  me  a  large  piece  of  rock,  the  surface  of  which 
exhibits  fine  parallel  lines,  which,  at  the  mine  (the  Hillside,  in  Ya- 
vapai  county,  Arizona),  were  called  striae.  The  rock  was  part  of 
the  casing  of  a  cavity  found  in  the  hanging-wall  of  the  lode,  which 
traversed  a  quartzose  talc-schist.  Its  surface  has  been  coveredj  by 
a  series  of  siliceous  coatings,  doubtless  deposited  by  the  mineral- 
bearing  waters  which  circulated  over  it.  The  precipitation  took 
place  along  certain  parallel  lines,  probably  marking  the  direction  of 
flow  of  the  circulating  waters,  and  the  resulting  appearance  is  to  be 
regarded  as  a  pretty  example  of  a  variety  of  crustification,  but,  com- 
ing as  it  does  from  a  lenticular  hole,  cannot  have  been  due  to  rub- 
bing caused  by  faulting. 

In  the  accompanying  drawing  (Fig.  1),  reproduced  from  a  sketch 
made  underground,  the  cavity  above  referred  to  is  marked  A.  There 
are  two  others,  B  and  F,  of  the  same  kind.  D  is  a  seam  6  inches 
thick,  of  white  talcose  gouge,  lining  the  footwall,  and  separating  it 
from  C,  which  is  the  lode  itself.  The  latter  is  15  to  18  inches  wide, 
and  consists  of  quartz,  iron  pyrites,  zincblende,  and  a  little  galena, 
very  much  intermingled,  and  carrying  gold  and  silver  in  almost 
equal  proportions.  The  lode  itself  reproduces  to  a  noticeable  extent 

*  Eng.  and  Min.  Jour.,  April  30,  Jane  11  and  18,  189  2. 

f  Bull.  Soc.  OeoL  de  France,  3  serie,  Feb.,  1891,  t.  xix.,  p.  313.  Compt.  rend 
Acad.,  t.  cxi.,  seances  du  24  Nov.  et  4  Dec.,  1890.  Compt.  rend.  Acad.,  t.  cxii.,  stance 
du  19  Jan.,  1891. 

J  As  shown  by  viewing  the  broken  edges  of  specimens. 


198 


THE   GENESIS   OF   ORE-DEPOSITS. 


the  structure  of  the  country-rock  which  it  has  replaced.  The  cavi- 
ties in  the  hanging-wall  are  also  surrounded  by  talc-schist,  which  is 
mineralized  to  such  a  degree  as  to  constitute  "  low-grade  ore."  The 
vein  cuts  clear  through  the  foliation,  nearly  horizontal,  of  the  talc- 
schist  and  the  alteration  of  the  country -rock,  while  most  marked  in 
C,  extends  to  a  varying  distance  on  either  side. 

Not  infrequently  the  quartz  of  a  lode  has  striated  markings  which 


c         D 


Fig.  I 

HILLSIDE  MINE,  ARIZONA 

are  but  the  negative  of  those  occurring  on  the  wall-rock.*  In  such 
cases  the  quartz  is  sometimes  entirely  solid  and  unbroken,  suggesting 
that  it  was  deposited  upon  the  previously  striated  surface,  and  that 
it  has  not  only  replaced  the  substance  but  also  reproduced  the  struc- 
ture of  the  rock  once  inclosed  by  the  fissure- walls.  On  the  other 
hand,  one  instance  may  be  cited  where  it  seems  necessary  to  suppose 
that  movement  took  place  subsequently  to  the  deposition  of  the 

*  Instances  of  such  are  to  be  seen  in  the  gold-quartz  veins  of  California. 


THE   GENESIS   OF   ORE-DEPOSITS.  199 

quartz.  At  the  1800-foot  level  in  the  Great  Extended  Hustler's 
mine*  at  Bendigo,  Australia,  the  quartz  lying  against  the  hanging- 
wall  of  the  reef  exhibited  a  surface  as  smooth  as  polished  ivory,  but 
distinctly  grooved,  and  also  marked  with  fine,  dark  lines,  parallel  to 
the  grooves.  The  latter  had,  I  believe,  an  origin  similar  to  that  of 
ordinary  striae,  while  the  dark  lines  were  due  to  the  grinding  of  par- 
ticles of  pyrite  observable  in  the  quartz.  Though  this  quartz  seemed 
to  the  eye  as  hard  as  adamant,  it  would  readily  crumble  away  when 
pressed  between  the  fingers.  It  had  been  crushed  to  the  consistency 
of  common  table-salt,  which,  save  for  the  presence  of  occasional  crys- 
tals of  pyrite,  and  for  its  highly  polished  surface,  it  much  resembled. 

Objection  has  been  raised  to  accepting  the  occurrence  of  clay, 
striae  and  slickensides  as  necessary  evidence  of  faulting,  because  they 
are  occasionally  absent  where  movement  may  be  supposed  to  have 
taken  place.  In  such  instances,  it  is  reasonable  to  infer  that  they 
have  been  destroyed  by  agencies  identical  with  those  to  which  the 
lode-formation  is  due,  namely,  the  replacement  of  country-rock,  often 
in  a  crushed  and  shattered  condition,  by  ore,  through  the  metamor- 
phic  action  of  percolating  solutions. 

There  is  a  fanciful  notion  current  among  miners  that  a  smooth 
wall  and  a  thick  gouge  are  the  necessary  adjuncts  of  a  productive 
"  true  fissure-vein."  Experience  does  not  confirm  this  belief.  A 
defined  wall  and  a  soft  seam  of  clay  are  naturally  welcome  to  the 
miner,  because  they  facilitate  the  actual  breaking  down  of  the  vein- 
stuff;  but  they  are  no  more  characteristic  of  productive  than  of  bar- 
ren lodes. 

The  irregularity  in  the  dip  of  some  veins  has  been  cited  as  dis- 
proving the  possibility  of  their  formation  along  lines  of  faulting. 
Occasionally  mine-workings  show  that  the  dip  of  a  vein  is  reversed; 
and  the  formation  of  the  fracture  which  it  occupies  cannot  be  re- 
ferred to  a  continuous  line  of  movement,  because  that  would  have 
involved  the  shearing-off  of  the  opposing  angle.  But  it  is  not  nec- 
essary to  suppose,  nor  do  facts  suggest,  that  lodes  are  generally  formed 
along  continuous  or  single  lines  of  movement.  As  Prof.  Posepny 
has  well  shown,  it  is  the  study  of  the  circulation  of  underground 
waters  which  affords  the  key  to  much  that  is  perplexing  in  ore- 
deposition.  In  such  cases  as  are  here  referred  to,  it  is  rational  to 
suppose  that  the  mineralizing  solutions  searched  out  the  easiest  way 
which  offered  itself.  They  did  not  necessarily  percolate  along  a  sin- 
gle definite  straight  line  of  fissuring,  but  often  deviated  from  it, 
*  See  Trans.,  vol.  xx.,  512  et  seq. 


200  THE   GENESIS   OF   ORE-DEPOSITS. 

whenever  it  afforded  a  less  ready  passage  than  was  offered  by  other 
fractures  which  united  with  it  or  crossed  it.  An  instance  which 
occurs  to  me  as  I  write,  is  furnished  by  the  Seven-Thirty  mine  at 
Silver  Plume,  Colorado.  The  lode  consists  of  a  system  of  veins 
carrying  rich  silver-ore.  The  most  productive  of  which  is  that 
which  bears  the  name  of  the  mine.  It  rarely  has  any  considerable 
width  ;  it  is  often  only  a  thread  traversing  the  coarsely  crystalline 
granitoid  gneiss  and  porphyritic  microcline  granite  of  the  region.  At 
the  third  level,  about  280  feet  from  the  surface,  there  is  a  very  marked 
irregularity  in  the  course  of  the  vein,  presenting  some  interesting 
features,  which  the  accompanying  sketch  (Fig.  2)  will  help  to  explain. 
From  the  shaft  eastward  for  several  hundred  feet  (A  to  B)  the 
vein  carries  ore ;  but  its  width  is  small  and  irregular.  The  lode 
widens  rapidly  at  B,  where  it  also  meets  with  a  sudden  deviation  in 
its  course.  At  a  first  glance,  this  looks  very  much  like  a  fault,  but 
subsequent  examination  will  correct  such  a  view.  The  fissure  con- 
tinues in  a  straight  line  from  K  to  L,  after  the  ore  has  swerved  to 


•H  O  P     Q 

Fig.  2 

SEVEN  THIRTY  MINE,  COLORADO. 

the  south.  Instead  of  maintaining  its  eastward  course,  the  ore  is 
disposed  in  two  cross-veins,  CD  and  EF,  nearly  at  right  angles  with 
that  course,  which  unite  with  a  fissure,  MQ,  similar  in  character  and 
parallel  in  strike  to  that  from  which  they  sprung,  AL.  Both  AL 
and  MQ  are  continuous  so  far  as  they  have  been  followed  in  the 
mine-workings.  The  walls  are  well-marked,  even  after  they  cease  to 
enclose  ore.  The  cross-veins  CD  and  EF  lack  well-defined  bounda- 
ries. The  western  branch,  CD,  is  a  streak,  about  3  inches  wide,  car- 
rying ore  of  a  tenor  of  300  ounces  of  silver  per  ton,  while  the  east- 
ern branch,  EF,  is  larger,  about  1  foot  wide,  and  carries  ore  of 
lower  grade,  about  100  ounces  per  ton.  The  latter  is  accompanied 
by  much  more  galena  than  the  former.  The  distance  between  the 
two  is  10  feet ;  their  length  is  44  feet.  The  country  separating 
them  is  not  noticeably  altered  or  mineralized. 


THE   GENESIS   OF   ORE-DEPOSITS.  201 

This  is  not  an  instance  of  faulting  ;  the  ore  is  found  in  connection 
with  a  system  of  fractures  AB,  CD,  EF  and  MQ,  the  varied  struc- 
ture and  arrangement  of  which  modified  the  circulation  of  mineral- 
izing solutions,  and  so  brought  about  the  irregularity  in  the  depo- 
sition of  the  various  minerals  comprising  the  ore.  The  mineralizing 
waters  met  with  diverse  conditions.  From  A  to  B  the  fissure  was 
tight,  and  its  boundaries  were  distinct,  limiting  the  circulation  to  a 
narrow  channel ;  hence  a  small  streak  of  ore  was  found.  At  B  the 
shattering  of  the  country-rock  accompanying  the  formation  of  the 
cross-fractures,  CD  and  EF,  offered  facilities  for  the  ready  penetra- 
tion of  the  solutions  and  for  chemical  interchanges.  From  C  to  D 
and  from  E  to  F  the  irregular  fracture  across  the  foliation  of  the 
country-rock  produced  irregular  but  rich  streaks  of  ore.  On  meet- 
ing with  the  other  main  line  of  fissure  the  solutions  again  found 
well-defined  boundaries  which  put  a  check  to  the  metamorphic  re- 
placement of  the  country-rock,  and  it  was  not  till  the  conditions 
changed  (at  O),  that  a  notable  width  of  ore  was  again  deposited. 

Many  supposed  faults  found  in  mine- workings  are  really  of  this 
character.  There  has  been  a  deviation  in  the  course,  and  a  marked 
diminution  or  increase  in  the  amount  of  ore-deposition,  because  the 
mineralizing  solutions  have  circulated  along  those  fractures  which 
presented  the  easiest  passage  and  offered  the  conditions  most  favora- 
ble to  chemical  interchanges. 

Returning  to  the  subject  of  striae,  slickensides  and  clay-seams,  I 
must  say,  that  while  the  questioning  of  accepted  theories  is  whole- 
some, and  the  views  quoted  above  deserve  respectful  consideration, 
it  seems  to  me  that  observed  facts  warrant  the  general  belief  that 
these  phenomena  have  usually  been  produced  by  the  rubbing  of  two 
faces  of  rock  which  have  undergone  movement;  and  I  do  not  sym- 
pathize with  those  who  consider  that  the  ordinary  explanation  is  far- 
fetched. We  know  that  the  rock-formations  of  1  he  upper  earth  have 
undergone  movement,  for  this  is  proved  by  all  geological  investiga- 
tion. Further,  we  have  every  reason  to  believe  that  movement 
among  beds  of  rock  of  unequal  flexibility  must  cause  some  to  break. 
Facts  confirm  such  a  belief.  Again,  every  break  must  be  coincident 
with  a  movement ;  for  a  fracture  can  hardly  be  said  to  exist  until 
made  evident  by  movement  however  slight.  At  any  rate  a  fracture 
unaccompanied  by  movement  would  not  give  the  relief  required  by  a 
series  of  beds  exposed  to  such  strain  as  necessitated  a  rupture.  Such 
movement  must  be  accompanied  by  friction,  due  to  the  tendency  to 
smooth  down  the  irregularities  of  the  two  opposing  rock-faces. 


202  THE   GENESIS   OF    ORE-DEPOSITS. 

Where  movement  has  once  occurred,  a  line  of  less  resistance  is  estab- 
lished, and  a  repetition  of  movement  is  likely.  The  result  is  to  break 
small  particles  from  off  projecting  points  and  so  form  a  dust  which 
water  makes  into  mud  or  clay,  also  to  scratch  the  surfaces  in  contact, 
forming  striae,  and  to  polish  them,  forming  slickensides.  Why 
therefore  deny  the  probability,  even  the  necessity,  of  the  movement 
of  the  walls  of  a  fissure,  and  why  endeavor  to  give  to  the  markings 
of  rocks  underground  an  origin  other  than  the  one  which  would  cer- 
tainly be  ascribed  to  them  if  they  were  found  on  rocks*  at  the  sur- 
face? 

The  pages  which  Prof.  Posepny  devotes  to  an  inquiry  into  the  con- 
ditions governing  the  flow  of  underground  waters  are  among  the 
most  valuable  of  his  treatise.  His  explanations  will  do  much  to 
clarify  our  conceptions  of  the  mode  of  behavior  of  underground 
waters,  and  will  doubtless  suggest  further  inquiry  in  the  same  di- 
rection. The  word  "circulation"  is  the  key  to  the  whole  matter. 
There  has  been  a  tendency  to  speak  of  descending,  lateral  and  as- 
cending currents,  as  though  the  one  adjective  would  cover  the  man- 
ner of  movement  of  all  mineral  solutions.  An  ascending  flow  was 
supposed  to  have  formed  this  lode,  descending  that  one,  while  others 
again,  steering  a  middle  course,  have  imagined  that  ore-formations 
derived  their  origin  from  solutions  having  a  lateral  flow.  In  each 
case  a  narrow  view  of  the  subject  is  both  unphilosophic  and  un- 
scientific; it  has  too  often  been  the  obstacle  to  progress  in  this 
branch  of  geology.  One  great  fact  confronts  us,  and  that  is  cir- 
culation. 

The  distinguished  author  is  himself  carried  away  by  his  preju- 
dices, and  in  the  latter  portions  of  his  treatisef  allows  his  ascen- 
sionist  views  to  lead  him  too  far  and  in  part  to  forget  the  very 
forcible  teaching  given  in  the  earlier  pages.  Much  will  be  done 
to  explain  the  many  puzzling  and  apparently  contradictory  feat- 
ures exhibited  by  the  ore-deposits  of  different  regions  if  we  remem- 
ber that  mineral  solutions  both  descend  and  ascend,  that  occasionally 
they  may  have  an  approximately  lateral  flow,  and  that  in  each  in- 
stance their  circulation  is  governed  by  a  diversity  of  ever-changing 
conditions. 

Water  must  first  descend  in  order  to  afterwards  ascend.  The 
known  density  of  the  earth  precludes  the  supposition  that  its  in- 

*  No  one  questions,  for  instance,  that  the  scratching  seen  on  boulders  from  a 
glacial  moraine  are  the  result  of  rubbing  due  to  movement, 
f  As  at  the  bottom  of  page  52. 


THE   GENESIS   OF   ORE-DEPOSITS.  203 

terior  contains  any  reservoirs  of  water;  the  sinking  of  deep  wells 
and  bore-holes  has  indicated  that  at  a  comparatively  short  distance 
from  daylight  the  temperature  is  so  high  that  water  could  not  exist 
as  such,  but  would  be  dissociated  into  its  constituent  gases ;  while 
actual  mining  exploration  has  shown  that  in  the  deepest  mines 
there  is  less  water  encountered  in  depth  than  in  proximity  to  the 
surface.  These  facts  all  confirm  the  every-day  observation  that  un- 
derground waters  originate  from  the  rain  and  snow  precipitated  from 
the  atmosphere. 

We  may  compare  the  circulation  of  water  up  and  down,  through 
the  earth's  rocky  exterior  to  that  of  the  ordinary  heater  in  a  house. 
The  water  circulates  because,  when  hot,  it  rises  through  the  length 
of  pipe,  and,  when  cool,  it  falls  back  to  be  reheated.  Using  this 
analogy  to  explain  Nature's  operations,  we  have  at  one  end  the  con- 
densation and  precipitation  of  moisture  due  to  a  fall  of  temperature, 
while  at  the  other,  and  deep  down  in  the  earth's  rocky  confines,  we 
have  a  heat  which  sends  the  water  back  to  the  surface.  In  this 
matter  of  ore-deposition  we  are  not  concerned  with  the  two  ends  of 
the  circuit.  We  have  no  particular  interest  for  the  moment  in  that 
part  of  the  water-circulation  which  intervenes  between  its  elevation 
by  evaporation  from  the  earth's  surface  and  its  return  as  rain ;  nor, 
on  the  other  hand,  can  we  see  what  goes  on  at  the  other  end  of  the 
circuit.  We  can  only  guess  what  conditions  obtain  and  what  phe- 
nomena occur  at  depths  inaccessible  to  man.  All  our  investigations 
must  concern  themselves  with  the  intermediate  stage,  that  stage 
which  is  most  particularly  marked  by  the  transition  from  higher  to 
lower  temperatures,  and,  inversely,  from  increasing  to  diminishing 
pressures.  It  is  the  nice  adjustment  of  these  conditions  which,  on 
the  one  hand,  favors  precipitation,  and,  on  the  other,  compels  solu- 
tion. To  the  miner,  therefore,  it  may  appear  most  important  to  in- 
vestigate those  factors  which  bring  about  precipitation,  because  to 
them  must  be  ascribed  the  immediate  agency  of  ore-deposition.  It 
would  simplify  his  ideas  if  he  could  speak  of  an  upper  zone  of  pre- 
cipitation, where  the  temperature  is  low  and  the  pressure  light,  in 
contradistinction  to  a  lower  region  of  solution,  where  the  heat  is 
great  and  the  pressure  intense.  Such  attempts  to  separate  the  lo- 
cality of  the  two  processes,  however,  must  not  be  carried  too  far. 
Precipitation  has  no  sooner  ceased  than  solution  begins.  It  is  the 
excess  of  the  one  over  the  other  which  causes  the  deposition  of  ore 
in  one  place  and  its  removal  to  another.  Similarly,  in  our  talk  of 
"  primary  "  and  "  secondary  "  deposits  of  ore,  while  some  such  dis- 


204  THE   GENESIS   OF   ORE-DEPOSITS. 

tinction  may  be  necessary  for  the  purpose  of  explaining  differences 
of  immediate  origin,  we  must  not  fail  to  recognize  that  all  the  ore- 
deposits  within  the  ken  of  man  are  essentially  secondary.  There  has 
been  nothing  original  since  the  world  was  first  evolved  from  chaos. 
We  have  to  deal  with  a  continuous  rearrangement  of  material.  The 
ore  of  one  place  came  thither  by  removal  from  another.  Whether 
it  be  present  in  minute  microscopic  particles  or  in  blocks  as  big  as  a 
house  is  a  distinction  more  economic  and  commercial  than  scientific 
and  philosophic.  The 'decomposition  of  one  mineral  is  required  for 
the  composition  of  another.  Ore-deposits  are  in  their  nature  con- 
centrations, whether  by  the  mechanical  accumulation  of  disin- 
tegrated fragments  of  older  deposits  or  by  the  local  regathering  or 
segregation  by  chemical  agencies  of  minerals  previously  widely  and 
minutely  disseminated,  or  finally  by  the  addition,  bit  by  bit,  through 
mechanical  and  chemical  force,  of  the  matter  brought  from  above 
or  below  by  circulating  waters. 

The  frequent  occurrence  of  thermal  springs  in  the  neighborhood 
of  later  eruptive  rocks  is  very  properly  emphasized  by  Prof.  Posepny, 
and  is  of  immediate  importance  to  the  student  of  ore-deposition 
because  the  eruptive  rocks  are  in  turn  found  so  often  in  close  associa- 
tion with  lode-formations.  That  thermal  springs,  eruptive  rocks 
and  ore-deposits  are  intimately  inter-related  in  their  origin  is  gener- 
ally accepted.  In  this  connection  I  may  be  permitted  to  contribute 
some  additional  facts. 

Besides  the  localities  quoted  by  Prof.  Posepny,  I  would  mention 
the  Hauraki  or  Thames  gold-field,  in  the  North  Island  of  New  Zea- 
land, where  a  good  opportunity  is  offered  for  the  study  of  this  sub- 
ject. In  the  Coromandel  peninsula  of  the  North  Island,  there  is  a 
gold-bearing  belt  extending  for  nearly  a  hundred  miles,  from  Cape 
Colville  to  Te  Aroha.  The  prevailing  country-rock  consists  of  Ter- 
tiary eruptives,  through  which  patches  of  Carboniferous  slate  occa- 
sionally appear.  There  are  thermal  springs  scattered  throughout 
the  region.  At  the  principal  mining  center,  the  Thames,  the  escape 
of  carbonic  acid  gas  has  often  caused  a  temporary  cessation  of  work 
in  the  mines.  There  are  soda-water  springs  in  the  vicinity  of  the 
Thames.  At  Te  Aroha,  at  one  end  of  the  gold -belt,  there  is  a  group 
of  celebrated  medicinal  hot  springs.  This  last  locality  is  connected 
by  a  continuous  chain  of  thermal  springs  with  Rotomahana,  about 
45  miles  distant,  the  famous  hot-lake  region,  the  pink  and  white 
sinter- terraces  of  which  were  known  for  their  beauty  throughout  the 
world,  until  Mt.  Tarawera  broke  out  in  sudden  eruption  and  destroyed 
them  in  1884. 


THE   GENESIS   OF   ORE-DEPOSITS.  205 

Veins  of  gold-bearing  quartz,  recent  eruptive  rocks,  thermal 
springs,  dying  solfataric  action,  and  active  volcanic  force,  are  all  in- 
timately associated  in  this  corner  of  the  world. 

At  the  Thames,  the  leading  mining  town  of  the  island,  bodies  of 
gold-ore  of  unusual  richness  have  been  found.  In  1871,  the  Cale- 
donia mine  produced  10  tons  of  gold  and  paid  three  million  dollars 
in  dividends.  In  1878,  at  the  Moanataeri,  5400  pounds  of  quartz 
yielded  14,600  ounces  of  gold.  The  prevailing  country-rock  is  an 
andesite  breccia,  traversed  by  zones  of  decomposition,  in  which  the 
gold-veins  occur.  At  Rotorua,  in  the  hot-lake  district  already 
referred  to,  the  plain  is  in  part  covered  with  fragmentary  andesite. 
This  material  is  usually  loose  and  uuconsolidated.  Near  the  edges 
of  the  fumaroles,  which  are  numerous,  it  has,  however,  become 
cemented,  and  then  very  much  resembles  the  country-rock  of  the 
mines.  The  rims  of  the  fumaroles  also  exhibit  products  of  decom- 
position, which  are  similar  in  character  to  those  observed  in  the  lode- 
channels  at  the  Thames,  and  which,  because  they  are  soft  and 
granular,  have  been  termed  "  tufaceous  sandstone."  Quartz  closely 
resembling  that  of  the  gold-veins  of  the  mines  can  also  be  seen  to  be 
deposited  around  certain  of  the  fumaroles  and  hot  springs  referred 
to  above.  My  examination  of  the  ore- occur  re  nee  and  vein-structure, 
though  incomplete,  led  me  to  conclude  that  the  deposition  of  the 
gold  and  its  associated  minerals  had  followed  certain  lines  of  altered 
country-rock  which  had  been  exposed  to  the  effects  of  dying  but 
lingering  solfataric  agencies.* 

Another  district  which  affords  evidence  to  help  us  in  studying  this 
subject  is  that  of  Pontgibaud,  in  south-central  France,  among  those 
volcanic  peaks  of  Auvergne  which  have  been  rendered  classic  by  the 
work  of  Poulet  Scrope.  The  silver-lead  lodes  of  this  district  have 
been  very  extensively  developed,  and  their  geological  structure  has 
more  than  once  received  notice  at  the  hands  of  competent  observers.f 
The  country-rock  consists  of  gneiss  and  mica  schist,  penetrated  by 
dikes  of  granulite.J  The  lodes  are  of  later  date  than  the  dikes,  but 
older  than  the  Pliocene  flows  of  basalt  which  cover  their  croppings. 

*  See  also  "Certain  Dissimilar  Occurrences  of  Gold-Bearing  Quartz"  by  the 
writer,  in  the  Proceedings  of  the  Colorado  Scientific  Society,  for  1893. 

f  Annales  des  Mines,  M.  Gue*nyveau,  1st  series,  t.  vii.,  p.  162  to  188.  MM. 
Kivot  and  Zeppenfeld,  4th  series,  t.  xviii.,  p.  137  to  257,  361  to  446.  Also  recently 
M.  Lodin,  April,  1892,  in  a  paper  entitled,  "Etude  sur  les  gites  metallifSres  de 
Pontgibaud,"  also  published  in  the  Annales  des  Mines. 

I  If  it  were  in  our  West  it  would  be  called  "  porphyry  " — a  term  which  has  gradu 
ally  been  losing  its  distinctive  meaning  through  careless  use. 


206  THE   GENESIS   OF   ORE-DEPOSITS. 

The  period  of  their  formation  is  considered  to  have  been  between  the 
middle  Miocene  and  the  middle  Pliocene,  very  probably  contempo- 
raneous with  the  extension  of  the  acid  eruptives  of  Mont  Dore,  which 
took  place  at  the  beginning  of  the  middle  Pliocene.  The  lodes 
generally  follow  the  veins  of  gran u lite,  and  are  productive  only  when 
so  associated.  When  the  dike-rock  in  which  the  lode  occurs  is  most 
feldspathic,  the  metalliferous  filling  is  most  valuable. 

In  this  region  mineral  springs  are  abundant,  and  the  escape  of 
carbonic  acid  gas  has  frequently  put  a  temporary  stop  to  underground 
work.  This  applies  particularly  to  that  part  of  the  district  through 
which  the  river  Sioule  flows  between  the  town  of  Pontgibaud  and 
the  mines  at  Pranal.  Often,  while  fishing  along  the  stream,  I  have 
noted  places  where  there  is  a  constant  escape  of  carbonic  acid  gas 
from  its  bed  to  the  surface.  At  Pranal  there  appears  to  be  an  inti- 
mate connection  between  the  lode-fissures  and  the  volcanic  vents. 
One  of  the  mineral  veins  has  been  traced  to  its  connection  with  what 
appears  to  be  a  vent  of  the  extinct  volcano  of  Chalusset.  Power- 
fully carbonated  springs  exist  close  to  the  mines  and  on  the  slope  of 
Chalusset. 

In  both  of  the  two  districts  above  cited,  the  one  in  New  Zealand 
and  the  other  in  France,  note  has  been  made  of  the  escape  of  con- 
siderable quantities  of  carbonic  acid  gas.  It  is  scarcely  necessary  to 
emphasize  the  fact  that  this  is  a  most  common  and  powerful  agent 
in  bringing  about  changes  in  rocks  and  minerals.  The  action  of  car- 
bonic acid,  and  of  the  alkaline  carbonates  which  it  forms,  have  been 
recognized  by  all  petrographers.  To  it  we  owe  the  salts  occurring 
in  ordinary  mineral  springs  ;  to  it  are  due  the  pseudomorphic  re- 
placement of  feldspar  with  chlorite*,  and  the  alteration  of  olivine 
into  serpentine,  and  of  limestone  into  dolomite.  Even  at  ordinary 
temperatures,  carbonated  waters  extract  magnesia  from  complex  sili- 


*  And  the  chlorite  afterwards  gives  place  to  tinstone.  This  is  a  subject  much 
studied  by  Mr.  Richard  Pearce,  at  a  time  when  its  importance  was  not  so  well  re- 
cognized as  now. — See  "  The  Influence  of  Lodes  on  Rocks,"  Proceedings  of  the 
Mining  Association  of  Devon  and  Cornwall,  September  8,  1864.  Mr.  Pearce  directs 
attention  to  the  difference  between  the  granite  encasing  the  lode  and  that  found  at 
some  distance  from  it.  He  makes  note  of  the  joints  in  the  granite,  and  remarks 
upon  the  difference  in  the  minerals  found  in  two  well-marked  systems  of  joints 
having  contrary  directions.  He  shows  that  the  changes  observed  in  the  rock  ad- 
joining the  lodes  have  their  origin  in  the  lodes.  Emphasizing  the  rnetamorphlsni 
of  the  granite  he  shows  that  the  lodes  consist  essentially  of  altered  granite,  the 
most  important  alteration  being  the  replacement  of  the  feldspar  by  chlorite,  by  tin- 
stone and  by  schorl.  He  discards  the  idea  of  an  igneous  origin  of  the  tin-ore,  and 


THE   GENESIS   OF   ORE-DEPOSITS.  207 

cates.  In  this  way,  biotite  loses  magnesia  and  iron,  becoming  con- 
verted into  muscovite. 

The  subject  of  the  close  association  of  ore-deposits  and  igneous 
rocks  is  a  most  important  one  to  mining  engineers.  The  detailed 
geological  surveys  of  several  of  the  most  productive  mining  districts 
of  the  West,  carried  out  during  the  past  few  years,  have  done  much 
to  emphasize  the  relation  which  seems  to  exist  between  bodies  of  erup- 
tive rocks  and  deposits  of  gold-  and  silver-ore  found  close  to  them. 
It  has  become  the  fashion,  especially  since  the  publication  of  Em- 
mons's  masterly  monograph  on  the  Lead vi lie  region,  to  suppose  that 
the  precious  metals  of  the  lodes  were  derived  from  the  leaching  of 
the  adjacent  eruptives ;  and  some  mining  engineers  have  gone  so 
far  as  to  consider  the  neighborhood  of  dikes  necessary  to  the  occur- 
rence of  a  productive  lode.  This  latter  notion  may  be  classed  with 
the  supposition,  now  slowly  passing  away,  which,  not  long  ago,  was 
so  strong,  that  a  "  true  fissure-vein  "  was  the  only  permanent  deposi- 
tory of  the  precious  metals. 

In  the  United  States,  in  Europe,  and  in  most  of  the  Australasian 
mining  regions,  the  close  association  of  dikes,  or  other  forms  of  in- 
trusive eruptive  rocks,  with  lode-formations  is  so  marked,  that  it  is 
not  surprising  to  find  such  rocks  considered  as  necessary  adjuncts  to 
the  occurrence  of  valuable  ore-deposits.  But,  generalizations  are 
proverbially  dangerous;  and,  that  this  is  an  illustration  of  the  pro- 
verb, the  following  facts  may  show. 

The  gold-mining  region  of  the  province  of  Otago,  in  the  South 
Island  of  New  Zealand,  is  confined,  for  the  most  part,  to  a  great 
series  of  foliated  quarztoze  schists  of  an  age  considered  Archaean  by 
some,  *  and  Silurian  by  others. f  These  rocks  have  an  enormous 
thickness  over  a  large  area;  the  thickness  has  been  estimated  at 
50,000  feet,  while  the  area  is  fully  10,000  square  miles.  This  has 
been  a  very  successful  gold-mining  region,  although  the  gravel-de- 
posits have,  so  far,  been  more  productive  than  the  quartz- veins.  The 
lodes  have  certain  well-marked  structural  peculiarities,  resulting 
from  the  foliated  arrangement  of  the  country-rock  which  they  tra- 

declares  that  aqueous  agency  alone  can  satisfactorily  account  for  the  changes  in  the 
rocks  and  the  formation  of  the  lodes.  He  expresses  the  belief  that  the  subject  of 
the  rnetamorphism  of  the  country-rock,  if  "diligently  investigated,  must  assist  in 
explaining  some  of  the  laws  which  regulate  mineral  deposits."  This  was  said 
thirty  years  ago! 

*  "  On  the  Foliated  Kocks  of  Otago,"  Professor  F.  W.  Hutton,  F.G.S.  Trans, 
of  the  New  Zealand  Institute,  vol.  xxiv.,  1891. 

f  "The  Gold-Fields  of  Otago."    Trans.  A.  I.  M.  E.,  xxi.,  412. 


208  THE    GENESIS   OF   ORE-DEPOSITS. 

verse.  In  a  previous  contribution,  incidental  reference  was  made* 
to  the  fact  of  the  remarkable  absence,  in  this  auriferous  area,  of  erup- 
tive rocks.  It  is  interesting  to  recall  so  marked  an  exception  to  what 
is  often  held  to  be  a  general  rule. 

That  the  quartzose  schists  of  Otago  are  simply  altered  sedimen- 
tary beds  of  very  early  geological  age,  there  is  little  reason  to  doubt. 
The  quartz  folia  are  arranged  along  the  lines  of  original  sedimenta- 
tion, and  not  along  cleavage-planes.  It  is  a  case  of  "  stratification- 
foliation,"  as  distinguished  from  "  cleavage-foliation."  f  The  only 
rock  likely  to  be  a  metamorphosed  eruptive  is  the  chlorite  schist  of 
Queeustowu.J  The  mining  regions  of  Otago  do  not  exhibit  any  of 
the  phenomena  of  contact-metamorphism  ;  and  the  changes  which 
have  been  produced  may  be  ascribed  to  what  we  call  "  regional  " 
raetamorphism,  a  vague  way  of  describing  those  alterations  which 
are  forever  taking  place  in  rocks  wherever  there  is  heat  and  pressure, 
alterations  which  are,  therefore,  most  evidenced  by  the  oldest  rocks, 
which  have  necessarily  been  overlaid  by  a  great  thickness  of  later- 
deposited  formatious.§ 

A  treatise  which  covers  so  wide  a  field  as  that  of  Professor  Po- 
sepny,  can,  of  necessity,  devote  but  scanty  attention  to  some  mining 
regions  which,  to  those  who  know  them,  appear  to  afford  important 
evidence  on  the  subject  of  ore-deposition.  In  this  regard,  it  is  to 
be  regretted  that  Professor  Posepny  does  not  seem  to  have  had  his 
attention  drawn  to  certain  very  excellent  geological  reports  contained 
in  the  blue  books  of  the  mining  departments  of  Victoria,  New  South 
Wales,  and  New  Zealand.  Australasia  has  many  object-lessons  to 
offer  to  the  student  of  economic  geology,  and  the  Colonial  geological 
surveys  have  published  several  accurate  and  most  interesting  descrip- 
tions of  them.  1 1 

*•  Trans.,  xxi.,  413. 

f  Prof.  T.  G.  Bonney  uses  these  terms  in  the  Quarterly  Journal  of  the  Geological 
Society,  vol.  xlix.,  part  1,  p.  95. 

J  As  pointed  out  by  Prof.  Button.    Op.  cit. 

I  I  do  not  lose  sight  of  the  fact  that  igneous  rocks  may  become  schistose  by  me- 
tamorphism,  especially  through  pressure,  as  a  dolerite  becomes  a  hornblende  schist. 
There  is  no  reason  to  suppose  that  such  a  metamorphism  has  occurred  in  these  rocks 
of  Otago. 

||  I  would  more  particularly  instance  The  Geology  of  the  Vegetable  Creek  Tin-Min- 
ing Field,  by  T.  W.  Edgworth  David,  and  the  recently  published  Special  Report  on 
the  Bendigo  Gold-Field,  by  E.  J.  Dunn,  together  with  the  numerous  observations 
made  by  R.  L.  Jack,  in  Queensland ;  H.  Y.  L.  Brown,  and  H.  P.  Woodward,  in 
South  Australia ;  G.  H.  F.  Ulrich,  and  F.  W.  Button,  in  New  Zealand ;  Wilkinson 
and  Liversedge,  in  New  South  Wales ;  Murray,  Sterling,  and  Howitt,  in  Victoria. 


THE   GENESIS    OF   ORE-DEPOSITS.  209 

In  concluding  this  contribution  to  the  discussion  of  Prof.  Po- 
sepny's  paper,  I  may  be  permitted  to  express  again  the  belief  that 
his  destructive  criticism  of  the  lateral-secretion  theory  is  most  op- 
portune, and  that  his  investigations  into  the  flow  of  underground 
waters  will  do  much  to  illuminate  our  views  of  the  methods  of  ore- 
deposition.  At  the  same  time,  I  cannot  but  hold  that  the  accumu- 
lation of  facts  and  observations  will  show  that  neither  the  lateral, 
nor  the  ascensionist,  nor  any  other  one  narrow  theory  can  cover  the 
multitudinous  diversity  of  the  ways  in  which  ore-deposits  are  found 
to  occur. 

E.  W.  RAYMOND,  New  York  City  :  Concerning  Mr.  Rickard's 
proposed  classification,  I  beg  to  say,  while  recognizing  its  conve- 
nience for  mining  engineers,  that  it  cannot  be  considered  as  a  substi- 
tute for  that  of  Prof.  Posepny,  for  the  simple  but  conclusive  reason 
that  it  is  not  genetic.  Its  fundamental  division  is  based  upon  the 
position  of  the  deposits,  which  should  be,  in  a  genetic  classifica- 
tion, a  subordinate  consideration  ;  and  the  most  profound  genetic 
distinction  presented  by  nature,  namely,  the  distinction  between  con- 
temporaneous and  subsequent  formation,  appears  in  this  scheme  as 
a  division  of  the  third  degree,  affecting  only  inclosed  bedded  deposits- 
If  I  were  inclined  to  criticize  names,  as  Mr.  Rickard  has  elsewhere 
done  with  regard  to  Prof.  Posepny,  I  might  point  out  that  the  word 
"contemporaneous"  does  not  describe  coal-beds,  which  Mr.  Rickard 
mentions  as  typical  examples  of  it.  Whatever  may  be  said  of  a 
coal-bed,  it  is  not  contemporaneous  in  origin  with  the  country-rock 
above  it  or  below  it.  But  this  is  a  small  matter.  The  point  I 
make  is  much  more  important,  namely,  that  the  classification  itself 
is  neither  based  on  genetic  distinctions  nor  on  any  other  logical  ar- 
rangement. I  say  this  all  the  more  frankly,  because,  as  Mr.  Rick- 
ard declares  in  complimentary  phrase,  he  has  largely  followed  the 
classification  given  by  me  in  1869.  But  that  was,  as  Mr.  Rickard's 
is,  merely  a  convenient  miners'  arrangement.  Now  that  Prof.  Pos- 
epny comes  forward,  proposing  for  the  purposes  of  science,  not  of 
mining,  a  truly  genetic  classification,  a  critic  may  fairly  demonstrate 
its  logical  defects  and  suggest  remedies,  or  declare  remedies  to  be  im- 
possible. In  the  latter  case,  his  contention  would  be  that  a  genetic 
system  cannot  be  constructed,  and  that  the  attempt  had  better  be 
abandoned.  But  to  say  that  one  prefers,  as  a  mining  engineer,  the 
handy  non-scientific  arrangement  of  ore-deposits  hitherto  in  use,  is 
no  criticism  at  all.  It  is  as  if  a  botanist,  considering  a  natural 
system  in  botany,  should  sap  that  it  was  discouragingly  complicated, 

14 


210  THE   GENESIS   OF   ORE-DEPOSITS. 

and  that  he  preferred  the  simple  ami  convenient  arrangement  of  Lin- 
naeus, by  which  one  could  identify  a  species  from  the  number  of  petals 
and  stamens  and  other  arbitrary  signs. 

H.  V.  WINCHELL,  Minneapolis,  Minn.:  While  heartily  agreeing 
with  the  frequently-expressed  opinion  that  Prof.  Posepny's  paper  is 
a  masterly  and  exceedingly  important  discussion  of  ore-deposits,  it 
still  appears  that  there  may  be  room  for  differences  of  opinion  on 
some  points.  Indeed,  they  necessarily  follow  from  such  decided 
statements  on  so  important  and  interesting  a  subject. 

Those  of  us  who  live  in  the  Lake  Superior  region  are  wont  to 
believe  that  we  have  some  conception  of  the  meaning  of  the  term 
"  ore-deposits."  We  can,  and  frequently  do,  point  with  pride  to  the 
great  value  of  our  production  of  iron-ore  and  the  fact  that  we  fur- 
nish nearly  two-thirds  of  the  total  product  of  the  United  States. 
It  is  an  industry  employing  about  30,000  miners  and  involving 
capital  to  the  amount  of  fully  $100,000,000.  But  when  we  come 
to  treatises  on  ore-deposits  we  are  always  disappointed.  We  find 
that,  while  speaking  generally  and  theoretically,  iron-ore  deposits 
may  be  mentioned,  yet  when  it  comes  to  critical  discussion,  and  the 
illustration  of  theories  by  examples,  they  are  omitted.  We  are  con- 
strained to  protest  that  "  ore-deposit "  does  not  signify  merely  a 
vein  of  gold-,  silver-  or  lead- ore  or  a  stock  work  of  tin-  or  zinc-ore, 
but  that  hematite  and  magnetite  form  ore-deposits  of  a  commercially 
important  and  genetically  highly  interesting  class. 

The  value  of  the  raw  iron-ore  produced  in  this  country  in  1889 
was  equal  to  the  value  of  the  gold  bullion  produced  in  the  same 
year.  And  if  we  take  the  value  of  the  pig-iron,  which  more  nearly 
corresponds  with  bullion  in  the  degree  of  removal  from  the  raw  ma- 
terial, we  find  it  equal  to  the  value  of  the  gold  and  silver  combined. 
And  yet  our  author  dismisses  the  entire  subject  in  a  couple  of  pages, 
and  of  Fuchs's  and  DeLau nay's  2000  pages  only  two  are  devoted  to 
the  most  important  iron-ore  district  on  the  globe. 

It  would  not  be  fair  to  suggest  that  iron-ores  are  overlooked  be- 
cause they  do  not  seem  to  be  explainable  by  the  theories  adopted 
for  other  classes  of  deposits.  If  that  were  the  case,  all  the  more 
need  of  giving  them  attention.  It  is  more  probable  that  it  is  be- 
cause of  the  recentness  of  their  development  and  the  comparatively 
scant  literature  on  the  subject  in  the  libraries  of  our  foreign  col- 
leagues. 

That  the  circulation  of  waters  carrying  different  chemical  reagents 
is  the  all-important  factor  in  the  genesis  of  ores,  as  we  find  and  mine 


THE    GENETS    OF   ORE-DEPOSITS.  211 

them,  is  clearly  shown  by  Prof.  Posepny,  and  is  accepted  by  the 
majority  of  writers  on  the  subject.  But  the  prominence  which  is 
given  to  ascending  waters  and  the  insignificant  effects  ascribed  to 
descending  solutions  will  not  find  such  ready  acquiescence.  It  seems 
likely  that  ascending  waters  are  the  more  likely  to  be  effective  and 
to  predominate  below  the  ground-water  level  than  in  the  vadose 
circulation.  But  it  can  be  conclusively  demonstrated  that  many  of 
the  immense  iron-ore  lenses  of  the  Lake  Superior  region  owe  their 
present  state  of  concentration,  even  to  the  depth  of  many  hundreds 
of  feet,  to  the  action  of  the  descending  waters.  Aside  from  the 
Mesabi  range,  the  proofs  lie  partly  in  the  following  well-known 
facts  : 

1.  The  ore  is  a   product  of  concentration  in  situ,  whether  the 
original  rock  or  lean  ore  was  an  oxide,  a  silicate,  or  a  carbonate,  or 
whether  it  was  oceanically  or  otherwise  precipitated. 

2.  The  ore-bodies  have  the  shape  of  highly-inclined  lenses,  and 
frequently  have  an  unaltered  "capping"  of  jasper  partially  cover- 
ing their  upper  ends. 

3.  When  this  capping  is  present,  it  can  be  traced  downward  into 
the  ore  through  changes  which  are  clearly  the  result  of  oxygenated 
atmospheric  waters. 

4.  The  downward  course  of  the  waters  is  further  shown   by  the 
protecting   action   of  dikes  and   other  impervious   barriers,  below 
which  the  ore  is  not  found. 

5.  The   ore-lenses   lie   in   basins  of   greenstone-schists   or   other 
rocks,  and  occur  at  various  depths  to  at  least  2000  feet. 

6.  At  the  lower  edges  of  some  of  these  lenses  are  found  deposits 
of  silica,  kaolin,  etc.,  which   have  plainly  been   removed  from  the 
ore-body  above  in  the  process  of  concentration. 

This  is  much  below  the  vadose  circulation,  as  the  immense  pump- 
ing engines  and  the  rivers  of  water  which  they  throw  the  year 
round  testify  ;  but  it  is  an  instance  of  the  formation  of  ore-deposits 
on  the  largest  scale  by  descending  waters. 

The  circumstances  are  somewhat  different  on  the  Mesabi  range, 
but  the  proof  is  no  less  clear  that  the  ore  has  been  formed  by  solu- 
tions percolating  downwards.  There  the  mines  lie  along  the  south 
side  of  the  continental  divide  or  water-shed,  from  which  waters  flow 
north  to  Hudson  Bay  and  south  to  the  Gulf  of  Mexico.  They  thus 
occupy  the  highest  regions  of  the  northern  part  of  the  State.  More- 
over, the  shape  of  the  strata,  and  the  presence  of  a  conglomerate 
beneath  them,  indicate  that  there  was  a  .shore-line  there  when  the 


212 


THE    GENESIS   OF   ORE-DEPoSITS. 


rocks  were  deposited.  These  facts,  with  the  comparatively  undis- 
turbed condition  of  the  strata,  lead  us  to  believe  that  the  conditions 
have  remained  during  many  geological  ages  as  they  were  originally 
and  as  they  are  now,  viz.,  such  that  the  inevitable  direction  of 
water-circulation  would  be  downward  and  following  to  a  certain  ex- 
tent the  gentle  dip  of  the  rocks  to  the  south. 

Although   of  remarkable  magnitude  and  chemical   purity,  these 


Taconite  from  the  Mesabi  range  changing  to  iron-ore  by  solutions  moving  from 
left  to  right,  a 6  is  a  fault  line  which  conducted  the  descending  waters  downward 
and  prevented  the  right  half  of  the  specimen  from  undergoing  -the  ferrification 
which  is  seen  in  the  left  half. 


deposits  are  essentially  surface-products  and  are  at  present  largely 
above  the  ground-water  level.  The  processes  of  replacement  by  the 
removal  of  silica,  and  of  concentration  by  the  addition  of  sesqui- 
oxide  of  iron,  can  be  seen  in  progress  in  a  hundred  places.  The 
rock  which  undergoes  this  change  is  a  gray,  reddish  or  greenish 
chert  ("  taconite ")  banded  with'  iron-ore.  Figs.  1  and  2,  taken 


THE   GENESIS   OF   ORE-DEPOSITS. 


213 


from  specimens  from  the   Mesabi,  illustrate  the  change   mentioned, 
and  show  the  downward  course  of  the  ferruginous  solutions. 

Since  we  have  here  examples  of  iron-ore  deposits,  both  above  and 
below  the  ground-water  level,  which  have  been  formed  by  descend- 
ing waters,  the  thought  naturally  arises  that  the  solutions  may  not 
have  been  so  universally  ascending  in  the  case  of  other  mineral  de- 
posits, as  our  author  would  have  us  believe. 


t  ta.  £ , 


Another  instance  of  partial  alteration  of  taconite  to  ore.  There  was  a  joint  here 
along  a  b  whence  downward  moving  waters  effected  a  more  rapid  change  for  some 
distance  laterally  than  the  solutions  percolating  toward  this  joint  along  the  strata 
from  left  to  right  were  able  to  produce  in  the  solid  rock.  Specimen  collected  by 
J.  E.  Spurr. 

Another  idea  on  which  undue  stress  seems  to  have  been  laid  is  the 
correctness  of  the  "  ascension  theory,"  and  the  absolute  error  of 
that  of  "  lateral  secretion.'7  A  consideration  of  these  two  ideas 
leaves  me  with  the  impression  that  they  are  not  in  reality  so  dia- 
metrically opposite  that  if  one  is  true  the  other  can  have  no  scin- 
tilla of  truth  in  it.  In  the  deep  region  the  circulating  waters  are 
supposed  to  be  under  considerable  pressure,  from  which  they  escape 
by  flowing  in  the  direction  in  which  they  meet  the  least  resistance. 


214  THE   GENESIS   OF   ORE-DEPOSITS. 

Even  if  the  solution  were  on  the  whole  ascending,  still  it  must  often 
happen  that  cracks  and  fissures  would  be  encountered,  leading  in  a 
lateral  direction  into  some  main  fissure,  full  of  ascending  waters 
under  slightly  less  pressure  than  that  behind  the  waters  which  entered 
laterally.  In  that  case  it  is  also  quite  likely  that  there  would  be  a 
different  chemical  reaction  at  or  near  the  junction  of  these  two  cir- 
culating fluids  from  that  produced  by  the  action  of  either  one  of 
them  on  the  rocks  through  which  it  passed.  This  might  result  in 
the  precipitation  of  certain  minerals  on  the  walls  of  the  main  fis- 
sure near  the  subsidiary  fissure,  and  thus  the  resulting  ore-deposit 
would  owe  fully  as  much  to  lateral  secretion  as  to  ascension.  And 
if  these  lateral  joints  and  cracks  (or  even  more  porous  rocks)  were 
sufficiently  numerous,  the  whole  vein,  when  formed,  would  be  due 
to  the  combined  actions  of  lateral  secretion  and  ascension. 

Moreover,  it  seems  almost  necessary  for  the  ascensionists  to  borrow 
aid  from  the  lateral  secretion  ists,  whether  they  will  or  no.  For  the 
question  arises:  Where  do  the  ascending  solutions  come  from,  any- 
how ?  Is  there  an  inexhaustible  reservoir  at  the  bottom  of  each  vein- 
fissure,  which  supplies  a  ceaseless  flow  of  carbonated  and  mineralized 
waters  carrying  precious  metals  in  solution  ?  Or  does  the  water  start 
from  the  surface  and  percolate  downward  until  it  is  forced  by  heat 
and  generated  gases  to  rise  again  ?  If  the  latter  is  the  true  suppo- 
sition, is  it  not  evident  that  the  fissures  which  conduct  these  ascend- 
ing waters  must  receive  them  from  all  sides  through  a  thousand  small 
crevices  and  pores,  thus  making  again  a  combination  of  both  lateral 
and  ascending  motions  and  depositions? 

If  ascending  waters  come  from  a  great  depth,  descending  waters 
must  reach  to  the  same  great  depth,  and  since  the  solutions  cannot 
traverse  the  same  path  in  their  ascent  that  they  do  in  their  descent 
there  must  be  a  certain  amount  of  lateral  motion  at  the  moment 
when  these  solutions  are  the  most  dense  and  carry  their  heaviest 
burden  of  dissolved  material.  And  it  is  evident  that,  whatever 
the  depth  from  which  the  metallic  elements  come,  there  is  as  much 
chance  for  one  mode  of  deposition  as  for  the  other. 


SECRETARY'S  NOTE. — The  remaining  contributions  to  the  dis- 
cussion published  in  this  volume  were  presented  at  the  Bridgeport 
Meeting,  October,  1894,  or  issued  with  the  papers  of  that  meeting', 
having  been  received  before  the  Florida  Meeting  of  March,  1895. 


THE   GENESIS   OF   ORE-DEPOSITS.  215 

PROF.  POSEPNY  (communication,  translated  by  the  Secretary) : 
First  let  me  express  my  warmest  thanks  to  all  those  who  have  so 
favorably  judged  my  paper  on  the  "Genesis  of  Ore- Deposits,"  and 
likewise  to  those  who  have  taken  this  occasion  to  bring  forward, 
whether  in  support  of  my  views  or  in  opposition  to  them,  various 
observations  and  opinions,  whereby  our  knowledge  of  ore-deposits 
has  been  unquestionably  increased. 

It  is  exceedingly  difficult — indeed,  almost  impossible — to  make  a 
correct  comprehensive  statement  of  a  subject,  the  separate  funda- 
mental data  of  which  are  scattered  throughout  the  world  ;  and  ray 
treatise  must,  of  course,  be  considered  as.  merely  an  attempt  in  that 
direction,  inspired  by  the  purpose  of  contributing  to  this  theme  an 
element  not  yet  sufficiently  recognized,  namely,  the  logical  applica- 
tion throughout  of  the  genetic  principle.  As  I  indicated  on  p.  8  of 
this  volume,  I  expected  as  a  result  neither  a  simplification  of  systems 
nor  a  direct  benefit  to  practice.  My  object  was,  irrespective  of  such 
considerations,  to  approach  more  nearly  to  the  truth. 

A  single  observer  may  be  able  to  establish  a  few  more  or  less  im- 
portant facts ;  but  the  great  mass  of  the  knowledge  required  he  can- 
not personally  possess.  In  the  most  favorable  case,  government 
institutions,  established  to  benefit  single  nations,  or  scientific  or  busi- 
ness associations,  may  procure  accurate  knowledge  of  the  mineral 
resources  of  separate  countries,  and  these  may  be  combined  to  in- 
crease the  knowledge  of  a  considerable  territorial  complex ;  but  the 
question  still  remains,  whether  the  developments  and  natural  ex- 
posures in  a  given  region  are  really  typical  and  conclusive  as  a  basis 
for  general  scientific  deductions.  In  this  respect,  an  international 
union  of  such  endeavors,  devoted  to  the  advancement  of  this  branch 
of  geology  would  be  a  decisive  gain. 

When  the  United  States  Geological  Survey  began  the  study  of  the 
geological  relations  of  ore-deposits,  there  was  ground  for  hope  that 
a  new  era  in  the  knowledge  of  this  subject  would  be  thereby  in- 
augurated. In  fact,  several  monographs  of  inestimable  value  con- 
cerning the  most  important  ore-deposits  had  been  published,  when, 
for  reasons  unknown  to  me,  the  whole  activity  of  the  survey  in  this 
direction  was  interrupted — an  event  much  to  be  lamented. 

Yet  a  monograph  can  give  only  what  is  revealed  by  the  develop- 
ments accessible  at  the  time  it  is  written  ;  and  since  mining  continu- 
ally makes  new  exposures,  and  for  the  most  part  obliterates  the  old 
ones,  a  complete  scientific  inquiry  should  involve  provision  for  the 
repeated  examination  of  a  given  mining  district,  and  for  publication, 


216  THE   GENESIS    OF   ORE-DEPOSITS. 

at  intervals  of,  say,  five  or  ten  years,  of  the  new  knowledge  thus 
acquired. 

It  is  scarcely  to  be  doubted  that  the  investigation  of  the  genetic 
relations  of  a  thing  is  necessary  to  complete  our  knowledge  of  it,  and 
that  this  inquiry  is  therefore  obligatory  as  a  part  of  the  study  of  any- 
thing which  we  desire  to  know  exhaustively.  Dr.  Raymond  (dis- 
cussion at  the  Virginia  Beach  Meeting,  p.  209)  has  defended  the 
introduction  of  this  principle  into  the  science  of  ore-deposits,  for 
which  I  thank  him  heartily. 

Messrs.  W.  P.  Blake  and  A.  Winslow  have  controverted  my  views 
concerning  the  original  source  of  the  lead-  and  zinc-deposits  of 
Missouri  and  Wisconsin,  condemning  at  the  same  time  the  similar 
views  brought  forward  at  the  same  Chicago  meeting  in  the  paper  of 
Dr.  W.  P.  Jenney.  Since  lam  personally  acquainted  only  through 
a  tourist's  journey  with  the  relations  of  these  deposits,  which  extend 
over  so  large  a  region,  and  am,  moreover,  not  master  of  the  wide 
literature  of  the  subject,  I  must  leave  the  defence  of  the  principles 
asserted  to  Dr.  Jenney,  and  will  here  simply  refer  to  his  reply,  con- 
tained in  the  present  discussion. 

With  regard  to  Mr.  Winslow's  observations,  I  must  confess,  that 
I  am  acquainted  neither  with  the  mine  at  Doe  Run  nor  with  the 
publications  of  Messrs.  Strong  and  Charnberlin.  But  I  know  that 
concerning  every  region  where  lead-  and  zinc-ores  occur  in  lime- 
stone and  dolomite,  the  two  opposite  theories  as  to  their  origin  in- 
variably appear ;  and  that  in  terranes  consisting  of  structural  pla- 
teaux, with  nearly  undisturbed  position  of  strata,  the  representatives 
of  the  view  that  these  ores  were  deposited  simultaneously  with  the 
country-rock  have  the  great  advantage  that  the  conditions  of  strati- 
fication are  in  their  favor. 

Besides  the  paper  here  in  discussion,  I  have  lately  devoted  to  the 
deposits  of  lead-  and  zinc-ores  in  soluble  rocks  a  special  treatise,*  in 
which  I  have  compared  the  occurrences  of  such  deposits  in  plateau- 
regions  with  the  conditions  obtaining  in  mountain  regions,  with 
already  disturbed  stratification.  This  publication  originated  in  an 
address  delivered  by  me  at  a  miners'  congress  in  Klagenfurt,  that  is 
to  say,  in  the  center  of  a  mining  industry  based  upon  mineral  occur- 
rences of  this  class. 

In  order  to  counteract  a  conception  based  upon  local  conditions,  I 
have  placed  side  by  side  the  various  alpine  occurrences  of  Carinthia 

*  "  Ueber  die  Entstehung  tier  Blei-und  Zinklagerstiitten  in  aufloslichen  Ge- 
steinen." — Jahrb.  d.  k.k.  Bergakademien,  1893. 


THE   GENESIS   OF   ORE-DEPOSITS.  217 

with  those  of  the  plateaux  of  Upper  Silesia  and  North  America, 
illustrating  them,  according  to  my  custom,  with  drawings  of  the 
typical  features.  Among  others,  the  occurrences  in  Sardinia  and  in 
the  North  of  England  are  discussed,  and  use  is  made  of  recent  litera- 
ture concerning  the  Upper  Silesian  plateau.  In  this  place,  I  can 
only  remark,  that  some  of  these  occurrences  in  the  mountain  terranes 
carry  evident  traces  of  the  subsequent  derivation  of  the  ores  from 
below  ;  and  that  this  fact  alone  is  an  argument  for  the  similar  origin 
of  the  plateau-deposits,  which  so  closely  resemble  the  former  in  all 
other  respects. 

The  treatise  I  have  mentioned  does  not  include  the  observations 
made  by  me  in  the  spring  of  the  present  year,  upon  the  analogous 
deposits  of  Laurium  in  Greece,  which  are  likewise  in  a  structural 
plateau  ;  but  I  can  assure  the  reader  that  the  developments  of  that 
region  also  indicate  the  derivation  of  the  ores  from  below. 

So  far  as  Mine  la  Motte  is  concerned,  I  can  attach  no  great  weight 
to  the  observations  which  I  made  there,  upon  a  hasty  journey. 
Nevertheless,  the  specimens  of  ore  disseminated  in  sandy  dolomite 
which  I  brought  away  show  distinctly  upon  the  surfaces,  after 
polishing,  the  secondary  intrusion  of  the  ore  into  the  country-rock. 

With  regard  to  Mr.  T.  A.  Rickard's  criticisms,  I  would  observe, 
that  formerly  the  theories  of  ascension,  descension  and  lateral  secre- 
tion were  generally  spoken  of,  without  the  assignment  of  any  cause 
for  the  assumed  movements  of  the  subterraneous  liquids.  I  think, 
however,  that  I  have  secured  some  definiteness  of  conception  by 
showing  the  actual  descent  of  the  vadose  circulation  and  the  ascent 
of  the  deep  circulation,  and  by  interpolating  the  lateral  movement 
between  the  two.  This  gives  reality  to  the  processes  formerly  con- 
ceived abstractly,  and  makes  it  possible  to  discuss  them. 

Mr.  Rickard  observes  that,  with  reference  to  the  formation  of  ore, 
I  have  laid  special  emphasis  upon  ascending  mineral  solutions 
(p.  176  of  this  volume).  I  meant  to  do  this,  however,  only  with  re- 
gard to  the  sulphides.  These  certainly  were  not  produced  from 
the  descending  solutions,  which  carry  oxygen  now,  as  they  unques- 
tionably did  in  former  geological  periods  also,  and  which  invariably 
decompose  sulphides  wherever  (as  is  the  case  in  the  vadose  zone) 
they  come  into  contact  with  them.  With  regard  to  the  sense  in 
which  I  use  the  terms  ascending  and  descending,  I  will  say  some- 
thing below. 

Mr.  Rickard  suggests  (loc.  eit),  that  since  the  increase  of  pressure 
and  temperature  favors  solution,  while  their  decrease  favors  precipi- 


218  THE   GENESIS   OF   ORE-DEPOSITS. 

tation,  precipitated  ores  are  to  be  expected  rather  in  the  shallow 
zone;  and  that  this  might  explain  the  circumstance  that  (as  he  be- 
lieves) ores  do  not  continue  in  depth.  Without  going  into  the  latter 
question  in  detail,  I  would  point  out  that  the  conceptions  of  shallow 
and  deep  are  only  relative,  and  that  in  my  discussion  I  could  only 
have  in  mind  the  conditions  existing  at  the  time  of  the  formation  of 
the  ores,  and  not  at  the  present  time.  What  was  once  shallow  may 
now  lie  very  deep,  and  vice  versa.  In  this  respect,  the  character 
of  the  ores  is,  I  think,  the  decisive  fact.  Oxidized  ores  must  have 
become  such  in  a  zone  then  shallow,  and  original  sulphides  must 
have  been  deposited  in  a  zone  then  deep,  and  beyond  the  reach  of 
oxidizing  agencies.  For  the  present,  only  the  extreme  of  these  pro- 
cesses can  be  clearly  recognized ;  but  it  is  not  impossible  that  future 
studies  in  this  direction  may  distinguish  the  characteristics  of  the 
intervening  stages  of  formation,  such  as  the  deposits  made  during 
lateral  movements  of  the  mineral  solutions. 

It  would  certainly  be  a  step  backwards,  to  allow  the  established 
characters  of  the  two  extremes  to  disappear  under  the  general  term 
"  circulation."  In  my  description  of  the  vadose  circulation  I  have 
pointed  out  that,  notwithstanding  its  course  at  the  ground-water 
level  appears  to  be  almost  horizontal,  and  notwithstanding  an  actual 
ascent  of  the  liquid  may  be  locally  brought  about  by  siphon-action, 
nevertheless  a  decided  prevailing  descent  can  be  proved  for  the 
vadose  currents.  The  terms  "  descending,"  "  ascending  "  and  "  lat- 
eral "  are  not  applied  to  a  portion,  but  to  the  whole  line  of  the  cur- 
rent; and  to  its  cause,  as  both  theoretically  and  empirically  deter- 
mined. I  cannot  admit  that  this  is  "a  narrow  view  of  the  subject," 
likely  to  hinder  progress  in  this  branch  of  geology;  on  the  contrary, 
I  believe  it  expresses  a  series  of  observed  facts,  calculated  to  increase 
our  knowledge. 

Mr.  Rickard  seems  to  look  at  every  new  conception  in  this  de- 
partment from  the  sole  standpoint  of  its  immediate  usefulness  in 
mining,  and  not  to  reflect  that  the  scientific  investigator  has  simply 
to  seek  the  truth,  without  regard  to  such  considerations.  His  criti- 
cism might  have  been  more  favorable  in  some  particulars  (e.g.,  Vir- 
ginia Beach  Discussion,  p.  202,  with  reference  to  p.  52  of  my  paper), 
if  I  had  taken  pains,  in  many  cases  in  which  I  was  speaking  of 
"ore-deposits,"  to  explain  that  under  this  phrase,  used  for  brevity, 
I  was  referring  to  deposits  carrying  metallic  sulphides. 

Mr.  H.  V.  Winchell  complained,  at  the  Virginia  Beach  meeting, 
that  under  the  head  of  ore-deposits,  the  deposits  of  iron -ore  are  too 


THE   GENESIS   OF   ORE-DEPOSITS.  219 

often  either  meagerly  or  not  at  all  considered.  This  complaint 
would  be  well-founded  as  against  a  report  on  the  mineral  resources 
of  a  given  region,  in  which  the  economic  importance  of  the  deposits 
is  a  controlling  element;  but  it  is  scarcely  just  in  its  application  to  a 
paper  like  mine,  which  was  intended  only  to  give  single  instances 
in  illustration  of  certain  genetic  theories.  The  reason  that  iron-ore 
deposits  generally  receive  comparatively  little  attention  in  genetic 
discussion  is,  I  think,  the  simplicity  of  their  conditions,  the  knowl- 
edge of  which  is  to  some  extent  assumed  to  be  familiar,  so  that 
authors  interest  themselves  much  more  in  the  discussion  of  the  more 
complicated  occurrences,  which  have  rarely,  as  a  rule,  been  correctly 
interpreted. 

I  am  indebted  to  Mr.  Winchell  for  making  good  my  omission  by 
adding  to  my  paper  his  account  of  iron-ore  deposits  known  to  him. 
Since  the  deposits  he  cites  consist  of  oxidized  ores  only,  they  may 
well  have  been  formed  by  an  originally  vadose  circulation.  I  must, 
however,  point  out  that  some  iron-ore  deposits  may  be  of  idiogenous 
origin.  Thus,  I  consider  the  oolitic  structure  of  some  deposits  (e.g., 
those  of  hematite  in  the  Silurian  of  Central  Bohemia)  as  a  sign  of 
their  original  deposition  in  the  basin.  I  have  had,  however,  far 
too  little  to  do  with  these  deposits  to  be  able  to  determine  more 
closely  the  significance  of  the  remains  of  brachiopods  (e.g.,  orthis 
shells),  which  occur,  transformed  into  hematite,  together  with  the 
oolites. 

The  iron-ore  beds  of  the  Silurian  basin  of  Bohemia  have  a  cer- 
tain analogy  with  those  of  the  Huronian  basin  of  Michigan,  especi- 
ally as  regards  the  length  and  continuity  of  their  outcrops  and  their 
connection  with  tufas  of  the  eruptive  rocks.  In  the  latter,  as  is  in- 
dicated by  the  beautiful  pseudomorphs  of  chlorite  after  garnet,  con- 
siderable metamorphosis  must  have  taken  place. 

Concerning  the  Mesabi  iron-ores,  I  am  indebted  to  this  critic  for 
the  illustrations  of  two  specimens  which  he  has  published.  They, 
indeed,  suggest  reflections  as  to  their  probable  genesis,  upon  which, 
however,  I  do  not  trust  myself  to  venture  at  this  time. 

In  reply  to  Mr.  WinchelFs  criticism  that,  while  laying  unneces- 
sary emphasis  upon  the  correctness  of  the  ascension-theory,  I  appear 
to  concede  to  the  theory  of  lateral  secretion  not  an  atom  of  truth,  I 
beg  to  observe : 

1.  That  I  deem  lateral  secretion,  in  the  sense  in  which  it  is  de- 
fined by  Professor  Sandberger,  to  be  possible  only  in  the  zone  above 
the  ground-water-level,  and,  therefore,  in  the  formation  of  oxidizec} 
ores  only,  and  not  for  sulphide-ores. 


220  THE   GENESIS   OF   ORE-DEPOSITS. 

2.  That  I  ana,  indeed,  obliged  (as. I  have  shown  on  page  26)  to 
assume  a  lateral  movement  of  liquids  in  the  deep  zone.  But  this 
is  a  region  in  which  present  processes  cannot  be  directly  observed, 
and,  therefore,  no  clues  to  the  conditions  of  deposition  are  found. 
Hence,  I  was  not  able  to  describe  such  conditions  in  my  paper.  It 
is  possible  that,  in  the  course  of  time,  conditions  of  deposition  may 
be  discovered  which  can  best  be  explained  in  this  way.  I  have  not 
yet  encountered  such  a  case. 

The  same  is  true  as  to  regions  in  which  the  two  extreme  branches 
of  the  subterranean  circulation  take  on  a  lateral  course.  The  case 
supposed  by  Mr.  Winchell,  in  which  a  deposit  can  be  ascribed  to 
ascension  and  also  to  lateral  secretion,  I  do  not  clearly  understand, 
since  a  physically  weaker  current  is  not  capable  of  displacing  a 
stronger  one.  While  the  extreme  forms  of  circulation — that  is,  both 
the  ascending  and  descending  branches — possess  a  pronounced  char- 
acter, it  must  be  expected  that  the  character  of  the  branches  con- 
necting these  extremes  will  be  less  distinct. 

Mr.  John  A.  Church  does  not  agree  with  me  regarding  ore-de- 
posits in  open  spaces  as  a  very  frequent  phenomenon,  and  expresses 
the  opinion  that  open  spaces  cannot  exist  at  great  depths  (such  as  3 
to  5  kilometers).  I  must  remind  him  that  in  order  to  establish  the 
first  proposition  the  most  important  observations  of  a  great  number 
of  observers  for  more  than  a  century  must  be  disproved.  He  can- 
not have  failed  to  notice  that  ore-deposits  of  that  form  which  has 
been  relatively  most  thoroughly  studied,  namely,  fissure-veins,  con- 
sist predominantly  of  separate  crusts,  often  marvellously  distinct, 
covering  what  were  once  the  walls  of  the  fissure-space.  Even  if  his 
proposition  be  confined  to  deposits  of  great  thickness  and  extent  in 
depth,  which  are  deemed  to  have  been  formed  (as,  for  instance,  the 
Comstock  lode,  which  he  has  studied)  by  substitution,  replacement 
or  metasomasis,  he  cannot  possibly  deny  the  existence  of  other  thick 
and  deep  deposits,  the  structure  of  the  ores  of  which  evidently  rep- 
resents the  filling  of  open  spaces.  For  instance,  some  of  the  Przibram 
veins,  which  have  been  worked  to  the  depth  of  more  than  1100  me- 
ters, and  the  ore  of  which  often  exceeds  10  meters  in  thickness,  must 
certainly  be  reckoned  as  wide  and  deep ;  yet  the  ores  from  their 
deepest  portions  do  not  differ  in  the  least,  so  far  as  structure  is  con- 
cerned, from  those  which  occur  in  the  shallower  parts.  Both  regions 
present  fragments  of  the  country-rock  of  all  sizes,  surrounded  by  the 
vein-material.  Moreover,  these  fragments  surrounded  by  quartz 
usually  predominate  in  one  or  the  other  of  the  crusts  of  the  vein- 
filling. 


THE   GENESIS   OF   ORE-DEPOSITS.  221 

Mr.  Church  seems  to  allow  small  value  to  the  observations  which 
it  is  possible  to  make  upon  the  ores  themselves  and  the  adjoining 
country-rock.  This  is  equivalent  to  the  rejection  of  the  only  means 
of  obtaining  data  concerning  their  probable  genesis.  It  is  difficult 
to  discuss  such  an  objection,  particularly  in  its  bearing  upon  the  phe- 
nomenon of  crustification,  which  I  consider  one  of  the  most  im- 
portant genetic  factors,  and  concerning  w<»ieh  I  will  speak  further 
in  connection  with  my  reply  to  other  critics. 

Mr.  Church  declares  the  Comstock  vein-mass  to  be  the  product  of 
substitution — that  is,  of  metasornatic  alteration — and  denies  entirely 
that  it  is  a  fissure-vein.  He  says  I  have  misunderstood  him  in 
saying  (p.  85  of  this  volume)  that  he  found  crusts  of  quartz,  alter- 
nating with  calcite,  in  the  Justice  mine.  The  passage  to  which  I 
referred  was  the  following  :  * 

"  The  ore  of  the  Justice  is  not  quartz  but  calcite,  with  but  an  insignificant  amount 
of  silica,  and  it  is  noteworthy  to  find  these  two  components  of  the  lode  dispersed 
in  that  banded  arrangement,  which  is  another  of  the  accepted  proofs  of  a  true  fis- 
sure-vein. The  quartz  is  always  on  the  propylite  and  the  calcite  on  the  quartz  ;  but 
there  is  no  comparison  in  respect  to  quantity.  The  quartz  is  always  insignificant 
in  thickness,  never  reaching  a  layer  more  than  an  inch  or  two,  so  far  as  noticed, 
except  in  the  dyke-vein,  while  the  calcite  forms  masses  which  are  several  yards  in 
thickness,"  etc. 

Why  is  this  not  what  I  call  crustification?  It  is  certainly  con- 
ceivable that  the  Comstock  was  formed  by  the  opening  of  a  space  of 
discission  at  the  contact  of  diorite  and  diabase,  the  filling  of  this 
space  by  the  deposition  of  silica  and  carbonate  of  lime  from  solu- 
tions, and  the  repetition  of  these  processes  until  the  deposit  had  at- 
tained its  present  thickness.  There  is,  for  example,  in  the  collection 
of  the  University  of  Vienna,  a  large  slab  from  the  Adalbert  vein 
at  Przibram,  showing  a  series  of  thin  galena- vein  lets,  the  crystals  of 
which  meet  in  the  axis  of  each  several  veinlet,  showing  that  each 
was  separately  filled,  and  hence  that  the  process  of  opening  and  fill- 
ing, regarded  with  reference  to  the  Adalbert  vein  as  a  whole,  was 
repeated  many  times,  until  the  aggregate  thickness  of  about  one 
meter,  shown  by  this  slab,  had  been  attained.  The  Comstock  might 
have  been  formed  likewise  by  repeated  opening  and  filling,  only  the 
several  fillings  would  have  to  be  thicker,  and  (since  the  material 
varied  little)  the  result  might  be  too  indistinct  to  attract  the  attention 
of  the  miner. 

Mr.  Church  regards  the  ore-body  of  the  Justice  mine  as  a  deposit 

*  The  Comstock  Lode,  etc.,  by  John  A.  Church,  New  York,  1870,  p.  173. 


222  THE   GENESIS    OF   ORE-DEPOSITS. 

separate  from  the  Comstock ;  but  it  is,  nevertheless,  a  branch  of  the 
Comstock  lode,  and  certainly  has  an  analogous  origin.*  The  occur- 
rence of  a  crustified  portion,  which  I  think  the  text  of  Mr.  Church's 
description  indicates,  possesses,  therefore,  significance  for  both 
branches  of  the  Comstock. 

By  crustification,  however,  I  do  not  mean  merely  a  lt  banded 
structure."  This  may  indeed  originate,  as  Mr.  Church  says,  in 
various  ways,  but  crustification  cannot ;  for  true  crusts  are  predomi- 
nantly chemical  precipitates,  the  crystal-aggregates  of  which  present 
a  certain  arrangement.  For  instance,  the  quartz-crystals  usually 
stand  perpendicular  to  the  former  cavity-wall,  directing  their  pyra- 
midal surfaces  towards  the  central  druse.  Incrusted  fragments  ex- 
hibit the  same  crusts  as  the  cavity-walls,  which  is,  at  the  same  time, 
an  additional  proof  of  the  existence  of  an  open  space,  etc.  It  is 
true,  that  among  these  chemical  precipitates  there  sometimes  occur 
mechanical  sediments,  such  as  frictional  detritus,  which  may  be  en- 
veloped by  one  or  another  of  the  crust-substances;  but,  this  is  by 
no  means  a  case  under  Mr.  Church's  statement  (p.  183  of  this 
volume) : 

"  Certainly,  a  banded  structure  can  arise  from  the  replacement  of  fragments  ar- 
ranged in  layers  by  pressure  and  friction,  as  well  as  in  many  other  ways,  and  does 
not  prove  deposition  in  a  cavity,  whether  filled  by  water  or  air." 

Pressure  and  friction  can  give  rise  to  no  arrangement  of  xeno- 
genites  in  separate  crusts;  in  other  words,  no  crustified  quartz  and 
calcite  filling,  such  as  I  suppose  to  exist  in  the  Comstock.  I  pos- 
sess, for  example,  besides  the  ores  from  the  Consolidated  Virginia 
bonanza,  mentioned  in  my  paper  (page  85),  some  quartz  specimens 
from  the  1500-foot  level  of  the  Belcher  mine,  in  which  separate 
dark  ore-bearing  zones  may  be  distinguished,  running  parallel  with 
each  other,  even  to  the  repetition  of  minute  undulations.  This  is, 
I  confess,  not  such  a  convincing  case  as  that  of  the  specimen  shown 
in  Fig.  53  of  my  paper,  which  exhibits  numerous  successive  crusts 
of  baryte,  fluorite,  etc.,  no  thicker  than  paper;  or  those  of  the  Raibl 
specimens,  which  consist  of  thousands  of  thin  layers  of  zincblende 
(whence  the  name  Schalenblende) ;  but  it  indicates,  at  least,  the 
probability  of  a  similar  origin.  It  is,  of  course,  not  in  every  ore- 
deposit  that  such  incontrovertible  proofs  as  those  last  mentioned 
are  found  and  preserved  for  science. 


See  Becker's  Geology  of  the  Comstock  Lode,  p.  30. 


THE    GENESIS   OF   ORE-DEPOSITS.  223 

Mr.  Church  points  out  (pages  182  and  183  of  this  volume)  that 
metasomatic  processes  effected  in  limestones  through  the  expulsion  of 
the  carbonic  acid  by  a  stronger  acid,  may  also  explain  the  exhala- 
tions of  carbonic  acid  so  frequent  in  certain  localities.  I  much  pre- 
fer, however,  to  avoid  the  adoption  of  such  a  purely  speculative 
standpoint,  and  would  only  suggest  that,  upon  that  view,  the  enor- 
mous volume  of  such  exhalations  in  volcanic  regions  would  require 
us  to  conclude  that  in  those  regions  immense  masses  of  limestone  are 
undergoing  the  metasomatic  process  referred  to. 

As  regards,  finally,  the  subsequent  alteration  of  the  original  ore- 
deposit,  which,  according  to  Mr.  Church,  partially  passes  into  hys- 
teromorphisrn,  it  is  undoubtedly  true  that  mineralogists,  devoted  to 
the  study  of  pseudomorphs,  have  collected  already  valuable  data  in 
this  field;  yet,  I  think,  prolonged  investigation  will  still  be  required 
before  general  deductions  can  be  profitably  discussed. 

Mr.  S.  F.  Emmons,  whom  I  have  to  thank  warmly  for  his  fav- 
orable judgment  upon  several  portions  of  my  paper,  naturally  does 
not  concur  in  the  views  I  have  expressed  concerning  Prof.  Sand- 
berger's  lateral-secretion  theory,  to  which  he  was  himself  atone  time 
more  or  less  committed. 

He  objects,  for  instance,  to  my  reference  to  the  barysphere.  This 
is  a  part  of  my  conception  of  our  planet  as  consisting  outwardly  of 
several  successive,  and  more  or  less  connected,  spherical  envelopes — 
atmosphere,  hydrosphere,  biosphere,  lithosphere,  and  barysphere — 
of  which  only  the  exterior  ones  are  open  to  our  direct  observation. 
In  discussing  the  mutual  reactions  of  these  great  geological  factors, 
which  we  may  briefly  call  aggregate-spheres,  it  is  unavoidably  neces- 
sary to  refer  to  the  barysphere,  which  is  beyond  our  observation  ; 
and,  according  to  my  habit,  I  have  used  this  term  in  speaking  of  the 
source  of  the  heavy  metals.  It  is  true,  the  term  is  only  a  device  to 
avoid  questions  still  unsolved  ;  but  the  same  may  be  said  concern- 
ing the  phrases  "  unknown  depths,"  or  "  unknown  sources  in  depth/7 
which  have  a  similar  meaning. 

It  seems  to  me,  that  Mr.  Emmons  and  others  of  my  critics  have 
not  correctly  understood  my  statements  concerning  the  several 
branches  of  the  underground  circulation  ;  and  I  therefore  beg  per- 
mission to  make  my  meaning  clearer,  even  at  the  cost  of  a  little 
repetition.  For  this  purpose,  I  will  take  for  illustration,  not  an 
ideal  case,  but  conditions  actually  existing,  namely,  those  developed 
at  Przibram,  concerning  which  there  exists  an  abundant  literature, 
shortly  to  be  increased  (in  the  second  volume  of  my  Archiv  fur 
praktische  Geologic)  by  a  monograph  of  my  own. 


224  THE    GENESIS    OF    ORE-DEPOSITS 

The  Przibram  district  lies,  in  round  numbers,  about  500  meters 
above  sea-level,  and  the  mine-workings  extend,  as  is  well  known,  to 
more  than  that  distance  below  sea-level.  The  ground-water  level  is 
but  a  few  meters  under  the  surface.  The  deepest  adit  drains  the 
mines  to  about  100  meters ;  and  everything  below  that  level  is 
strictly  deep  workings,  from  which  the  water  is  lifted  to  the  adit- 
horizon.  A  comparison  of  the  water  raised  from  different  levels 
shows  that  the  largest  quantities  come  from  the  upper  ones,  and  that 
the  amounts  diminish  with  increasing  depth,  so  that  at  about  300 
meters  below  sea-level  no  water  remains  to  be  raised,  the  ruling  rock- 
and  air-temperature  of  about  23°  C.  (74°  F.)  at  that  depth  sufficing 
to  evaporate  the  small  existing  quantity  of  water.  This  is  certainly 
a  striking  proof  that  the  water  encountered  in  mining  is  of  atmos- 
pheric origin. 

The  ore-deposits  are  steeply-dipping  fissure-veins,  which  are 
mined  by  reason  of  their  richness  in  silver  (about  5  per  cent.,  or  50 
kilos  per  metric  ton — or  say  1458  ounces  Troy  per  ton  of  2000 
pounds  avoirdupois).  Even  in  the  neighborhood  of  the  surface  the 
sulphides  predominated,  but  were  mixed  with  a  great  variety  of 
beautiful  minerals,  which  have  made  Przibram  famous  among  col- 
lectors, and  most  of  which,  according  to  the  results  of  the  investiga- 
tions of  F.  A.  Reuss  and  others,  are  of  secondary  origin.  It  can- 
not well  be  doubted  that  this  alteration  is  due  to  the  oxidizing  prop- 
erties of  the  liquids  coming  from  the  surface.  But  this  variety  of 
minerals  is  confined  at  Przibram  to  the  upper  zones.  Since  mining 
has  penetrated  to  lower  levels,  its  product  has  been  mainly  only  rich 
argentiferous  galena,  with  accompanying  zincblende,  etc.  The  dimi- 
nution in  secondary  minerals,  so  far  as  it  can  be  determined,  seems 
to  follow  closely  the  progressive  diminution,  in  depth,  of  the  quan- 
tity of  surface-waters. 

Concerning  the  origin  of  the  secondary  alterations,  there  is  (as  Mr. 
Church  may  be  pleased  to  know)  110  doubt  at  Przibram.  The  only 
question  at  issue  concerns  the  explanation  of  the  original  vein-filling, 
consisting  of  sulphides.  This  must  have  come,  of  course,  from  some 
rock  as  a  source;  and  on  this  point  views  are  at  variance. 

1.  Professor  Sandberger  at  first  conceived  that  this  filling  came 
directly  from  the  country-rock  (Nebengestein).  The  technical  term 
Nebengestein  is  more  definite,  perhaps,  than  "  country-rock."  Ifc. 
means  literally  the  rock  alongside,  or  the  country-rock  or  wall-rock 
immediately  in  contact  with  the  deposit.  In  this  sense,  it  is  impos- 
sible to  conceive  of  any  other  process  than  that  of  lateral  secretion, 
which  could  make  the  Nebengestein  the  source  of  the  filling ;  and  I 


THE   GENESIS   OP   ORE-DEPOSITS.  225 

have  attempted  in  my  paper  to  show  the  improbability  of  such  a 
lateral  secretion  of  such  a  filling. 

2.  Mr.  Emmons,  in  his  paper  on  "  The  Geological  Distribution  of 
the  Useful  Metals  in  the  United  States,"  read  at  the  Chicago  meet- 
ing (Trans.,  xxii.,  53),  has  connected  the  derivation  of  the  various 
metals  of  different  deposits  with  the  observed  geological  conditions 
of  that  country,  discussing  the  metals,  iron,  manganese,  nickel,  tin, 
copper,  lead  and  zinc,  mercury  and  gold  and  silver  separately.  In 
his  criticism  of  my  views  in  this  field  (pages  185  and  186  of  this 
volume),  he  has  taken  occasion  to  express  a  general  statement  for 
all  ore-deposition.  According  to  his  opinion,  the  metallic  con- 
stituents were  derived  by  lateral  secretion  from  rocks  within  "rea- 
sonable proximity ;  "  and  "  ore-bearing  currents  may  in  such  cases 
have  had  an  upward,  downward  or  lateral  motion,  according  to 
differing  local  conditions  of  rock-structure.7'  This  latter  expression 
I  would  like  to  amend  in  accordance  with  the  fact  that,  while  the 
local  conditions  of  rock-structure  indeed  influence  the  movements  of 
liquids,  the  true  causes  of  the  upward,  downward  and  lateral  motion, 
as  explained  in  my  discussion  of  this  point,  lie  outside  the  particu- 
lar rock- structure. 

I  would  invite  Mr.  Emmons  to  take  the  standpoint  sketched  on 
pages  51  and  52  of  this  volume,  in  the  depths  of  the  Przibram 
mines,  and  see  how  he  would  get  along  with  his  assumption  of  lateral 
movement.  And  I  must  repeat  that  it  is  not  so  much  the  local  di- 
rection of  the  currents,  as  the  general  character  and  cause  of  the  flow 
which  should  be  kept  in  view. 

The  general  phenomenon  of  descending  currents  in  the  Przibram 
mines  is  clearly  subsequent  to  the  formation  of  the  ore-deposits  ;  and 
the  existence  of  lateral  movements  of.  the  vadose  circulation  which 
could  form  these  deposits  is  inconceivable.  Let  us  see,  then,  whether 
such  movements  could  occur  in  depth,  in  the  sense  defined  by  me 
on  p.  26  of  this  volume,  and  quoted  by  Mr.  Emmons. 

We  should  be  forced  to  assume  that  the  open  vein-channels  had 
not  extended  much  deeper  than  the  point  (500  to  700  meters  below 
sea-level)  at  which  I  have  invited  Mr.  Emmons  to  stand,  and  also 
that  there  was  no  special  upward  tendency  of  the  waters  filling 
these  channels.  A  lateral  continuous  movement  would  be  only  pos- 
sible if  there  was  something  "  in  reasonable  proximity "  which 
would  consume  the  moving  current,  or  force  it  back  to  the  surface. 
To  expect  this  phenomenon  in  a  terrane  already  traversed  by  chan- 
nels reaching  to  the  surface  is  irrational.  In  the  only  conceivable 

lo 


226  THE   GENESIS   OF    ORE-DEPOSITS. 

sense,  it  would  merely  make  the  lateral  movement  an  incidental  part 
of  a  general  upward  circulation.  But  this  favors  my  view  of  the 
ascent  of  mineral  solutions  from  greater  depths  than  have  yet  been 
reached  in  mining,  i.e.,  from  "  unknown  depth,"  as  Mr.  Emmons 
expresses  it,  or  from  the  barysphere,  as  I  have  expressed  it.  He 
also,  by  the  way,  assumes  the  origin  of  the  heavy  metals  from  the 
barysphere  (or  "  from  the  depths/'  as  he  prefers  to  say),  and  goes  so 
far  as  to  intimate  that  I  would  make  the  theory  more  plausible  by 
allying  it  with  that  of  Vogt,  according  to  which  a  process  of  so- 
called  differentiation,  during  the  cooling  of  the  eruptive  rocks,  has 
concentrated  their  metallic  contents  in  certain  regions  more  or  less 
accessible  to  our  observation.  For  my  part,  I  must  wait  until  Vogt's 
ideas  have  assumed  a  more  solid  form  ;  but  I  cannot  help  suspecting 
that  Mr.  Emmons  favors  them  principally  because  they  bring  the 
concentrated  metals  in  eruptive  rocks  within  the  reach  of  lateral 
secretion,  as  a  forming  process  for  ore-deposits. 

Mr.  Emmons  doubts  my  conclusion,  based  upon  Noggerath's  ob- 
servations, that  waters  rising  under  pressure  are  capable  of  creating 
a  channel  for  themselves  in  soluble  rocks.  In  this  connection  I 
must  refer  to  the  difficulty  encountered  in  explaining  the  cavities 
containing  pipes  of  ore  in  soluble  rocks.  In  my  monograph  on 
Resbanya,*  published  when  Noggerath's  work  was  unknown  to  me, 
I  was  forced  to  assume,  as  the  cause  of  the  formation  of  the  cavity, 
the  downward  vadose  currents,  and  as  the  cause  of  the  filling,  on  the 
other  hand,  the  ascending  currents  of  the  deep  circulation  ;  in  other 
words,  two  processes,  representing  the  extremes  of  circulation,  and 
successively  acting  along  the  same  line.  Such  a  dilemma  may  be 
presented  by  any  ore-deposit  in  limestone.  Indeed,  I  became 
acquainted  subsequently  with  instances  indicating  that  the  two  pro- 
cesses of  cavity-forming  and  cavity-filling  may  have  been  sometimes 
almost  simultaneous.f  I  was  greatly  pleased  when  I  learned  of 
Noggerath's  observations  and  deductions,  and  I  took  pains  at  that 
time  to  acquaint  Mr.  Emmons  by  letter  with  the  consequent  change 
in  my  own  views.  The  observation,  as  I  convinced  myself  in  1885, 
cannot  now  be  verified,  for  the  whole  place  at  Burtscheid  is  com- 
pletely built  over;  but  Noggerath  was  a  highly  conscientious  ob- 


*  Geologisch-montanistische  Studie  der  Erzlagerstatlen  von  Rezbanya,  in  S.  Unyani. 
Published  by  the  Hungarian  Geol.  Soe.,  Budapest,  1874. 

t  See  my  paper  in  Jahrb.  der  k.  k.  Bergakad.,  1893,  p.  18,  '*  Ueber  die  Etistehuiig 
der  Blei-  und  Zinklagerstatten  in  aufloslichen  Gesteinen,"  especially  Fig.  14,  PI. 
III. 


THE   GENESIS   OF   ORE-DEPOSITS.  227 

server,  and  there  can  be  no  doubt  of  the  correctness  of  his  statement 
of  the  facts.  Moreover,  the  phenomenon  is,  a  priori,  inevitable.  If 
the  highly  dilute  currents  of  the  vadose  circulation,  descending  by 
gravity,  can  eat  out  their  own  channels  in  salt  or  limestone  (as  is 
shown  at  p.  19  and  other  places  in  my  paper),  all  the  more  might 
such  effects  be  expected  from  waters  ascending  under  pressure  and 
more  highly  charged  with  reagents.  Fig.  9  of  my  paper,  showing 
the  wedge-shaped  spaces  of  corrosion  described  by  Daubree  from 
Bourbonne-les-Bains,  with  their  summits  directed  upward,  gives  ac- 
tual proof  of  this. 

My  reference  to  the  wedge-like  form  of  certain  deposits  at  Lau- 
ritirn  was  based  on  an  ideal  profile.  In  the  spring  of  the  present 
year  (1894)  I  personally  visited  the  district,  and  strove  to  secure 
more  accurate  drawings  of  the  position  and  form  of  the  deposits.  I 
must  confess  that  I  was  not  able  to  find  any  such  drawings,  and  I 
must  therefore  submit  to  the  rebuke  of  Mr.  Emmons.  So  far  as  I 
know  the  literature  concerning  the  Laurium  district,  the  only  accu- 
rate drawings  are  those  of  the  French  company  in  the  treatise  of 
A.  Cambresy.*  (1  take  this  opportunity  to  correct  a  typographical 
error  in  the  pamphlet  edition  of  my  paper.  Fig.  87  was  taken,  not 
from  Cordelia  but  from  Huot.) 

With  regard  to  the  essential  difference  of  opinion  concerning  the 
Leadville  deposits,  I  may  observe  that  the  reason  I  ventured  to  dis- 
cuss that  district  without  having  personally  studied  it,  is  to  be  found 
in  the  magnificent  monograph  of  Mr.  Emmons,  the  interesting  con- 
ditions which  it  describes,  and  its  contradiction  of  current  views  as 
to  the  origin  of  the  Leadville  ores.  Passing  by  all  corrections  and 
criticisms  on  points  of  minor  importance,  I  wish  only  to  keep  in 
view  this  essential  difference  of  opinion,  and  to  inquire  what  were 
the  convincing  reasons  which  led  Mr.  Emmons  to  assert  in  this  case 
a  descent  of  the  mineral  solutions. 

He  separates  the  sources  of  the  metallic  substances  into  "  imme- 
diate "  and  "  ultimate."  The  latter,  by  reason  of  their  purely  spec- 
ulative nature  he  does  not  discuss,  but  devotes  himself  to  the  former. 
Without  being  able  to  doubt  that  these  substances  originally  came 
from  great  depths,  and  without  being  willing  to  assert  that  they 
came  wholly  from  the  country-rock  actually  adjoining  the  deposits, 
he  believes : 

1 .  That  they  came  from  above. 

*  "  Le  Laurium,"  par  A.  Cambresy,  Rev.  Univ.  des  Mines,  3  ser.,  t.  vi.,  1889. 


228  THE   GENESIS   OF   ORE-DEPOSITS. 

2.  That  they  were  derived  chiefly  from  neighboring  rocks. 

With  regard  to  the  first  of  these  propositions  I  can  find  in  his 
elaborate  monograph  no  tangible  proofs  whatever,  only  conclusions 
deduced  from  certain  observations.  The  shape  and  position  of  the 
ore-deposits,  whether  of  those  at  the  contact  between  porphyry  and 
lime,  or  those  in  the  limestone,  afford  no  conclusive  proof  of  descend- 
ing mineral  solutions  as  their  source.  Indeed,  this  is  disproved  by 
the  fact  that  the  deposits  were  originally  sulphides  (as  they  are  now 
shown  still  to  be  at  greater  depths),  and  such  sulphide-deposits  can- 
not be  asserted  to  have  been  formed  by  solutions  descending  from 
the  surface  (unless  such  an  application  should  be  made  of  the  case 
cited  on  p.  98  of  my  paper,  namely,  the  reduction  to  sulphides  by 
means  of  organic  matter).  The  interior  structure  of  the  deposits  and 
of  the  country-rock,  so  far  as  they  are  described  in  the  publications 
on  the  subject,  likewise  fail  to  furnish  any  conclusive  proof  of  this 
assumption. 

In  his  re-examination  of  the  mines  in  1890,  Mr.  Emmons  found, 
even  in  the  original,  unaltered  sulphide-ores,  no  crustification,  from 
which  he  concludes  that  in  this  case  there  has  been  no  deposition  of 
ore  in  open  spaces,  but  a  metasomatic  replacement  of  the  limestone. 
It  is  to  be  hoped  that  investigations  on  this  point  will  not  be  wholly 
abandoned  in  future.  Mr.  Emmons  mentions  also  his  recognition  of 
the  granular  structure,  joints  and  cleavage  of  the  original  limestone 
in  the  sulphide-ores  of  the  A.  Y.  and  Minnie  mines,  and  speaks  of 
the  cracks  in  the  top  of  the  ore- body,  "  through  which  the  ore-bear- 
ing solutions  had  descended."  This  is  clearly,  as  stated  in  this  form, 
an  expression  of  opinion.  A  detailed  and  purely  objective  descrip- 
tion, particularly  if  accompanied  with  drawings,  would  be  highly 
valuable,  and  might  constitute  the  tangible  proof,  the  absence  of 
which  I  have  pointed  out.  Mr.  Emmons  gives  us  ground  to  hope 
for  further  observations  in  this  direction,  based  upon  the  latest  de- 
velopments of  the  mines.  For  the  present,  however,  it  cannot  be 
said  that  we  have  any  decisive  proof  from  the  interior  structure  of 
these  deposits. 

The  facts  described  in  the  literature  concerning  Leadville  may 
be  equally  well  used  in  support  of  the  ascension-theory.  As  I 
have  remarked  (page  98  of  this  volume),  the  ores  were  at  first  con- 
ceived to  occur  at  the  contact  between  porphyry  and  limestone,  or 
confined  to  the  lime;  but  afterwards  it  became  clear  that  not  the 
whole  contact-surface  as  such,  but  only  certain  zones  of  it,  could 
be  regarded  as  the  principal  centers  of  the  accumulation  of  ore. 


THE  GENESIS   OP  OEE-DEPOSITS.  229 

These  ore-shoots,  lying  in  and  near  the  contact-plane,  were  the 
channels  of  which  the  mineral  solutions  availed  themselves.  A  par- 
allel is  thus  furnished  to  various  other  ore-deposits ;  for  instance,  the 
zinc-  and  lead-deposits  of  the  Alps,  the  shoots  of  which  are  near  a 
contact  of  soluble  with  insoluble  rock,  and  pursue  the  same  direc- 
tion as  the  stratification.*  For  the  establishment  of  this  analogy, 
credit  is  due  to  the  mining  engineers  who  have  published  their  ob- 
servations at  Leadville,  and,  as  Mr.  Emmons  observes,f  have  ren- 
dered valuable  assistance  in  enlarging  our  knowledge  of  the  facts  as 
developed  by  mining. 

The  text  of  Mr.  Ernmons's  great  monograph  on  Leadville  shows 
plainly  (p.  572)  that,  under  the  impression  produced  by  the  first 
publication  of  Professor  Sandberger,  the  author  deemed  the  as- 
cension-theory to  have  been  already  completely  overthrown.  He 
assumes  that  the  type  of  a  vein,  as  described  by  earlier  authorities, 
is  a  purely  ideal  conception,  and  does  not  exist  in  nature.  To  show 
that  these  writers  had  before  them,  on  the  contrary,  a  real  condition, 
I  have  cited  the  developments  at  Przibr'am.  If  we  substitute,  in 
that  case,  for  the  space  of  discission  the  spaces  occupied  by  the  Lead- 
ville deposits,  the  situation,  as  concerns  the  question  of  the  direc- 
tion of  the  ore-bearing  circulation,  is  not  altered.  The  flat  dip  of 
the  ore-shoots  and  the  solubility  of  the  country-rock  at  Leadville 
are  scarcely  decisive  as  to  this  question.  Nor  does  the  depth  thus 
far  attained  in  Leadville  mining  afford  conclusive  evidence.  In  my 
judgment,  therefore,  notwithstanding  the  differences  between  Przi- 
bram  and  Leadville,  the  same  inference  must  be  drawn  in  both  cases 
as  to  the  direction  of  the  ore-bearing  circulation.  In  other  words, 
Leadville  must  be  declared  to  be  no  exception  to  the  general  rule 
that  ore  deposits  carrying  metallic  sulphides  have  been  formed  by 
ascending  solutions. 

Whether  the  metallic  contents  were  derived  wholly  or  predomi- 
nantly from  the  eruptive  rocks  adjacent  to  the  deposits  or  occurring 
within  a  certain  distance,  is  an  independent  question. 

Mr.  G.  F.  Becker's  criticism  (page  189  of  this  volume),  having 
been  prepared  without  opportunity  for  a  thorough  combination  of 
authorities,  is  considered  as  preliminary  only.  It  deals,  as  does 
that  of  Mr.  Emmons,  in  the  main,  with  metasomatic  forma- 

*  See  my  treatise  (1893),  already  cited,  on  the  "  Origin  of  Lead-  and  Zinc-De- 
posits in  Soluble  Rocks." 

f  Page  188  of  this  volume.  See  also  "The  Mining  Work  of  the  U.  S.  Geol. 
Survey,"  Trans.,  x.,  412  et  seg. 


230  THE   GENESIS   OF   ORE-DEPOSITS. 

tions,  without  reference  to  formations  in  open  spaces,  and,  con- 
templating the  former  exclusively,  seems  to  disparage  the  em- 
phasis which  I  have  laid  upon  crustification  as  a  clear  proof  of 
the  filling  of  open  spaces.  According  to  his  view,  the  recogniza- 
bility  of  successive  deposits  is  dependent  upon  incidental  local  cir- 
cumstances, but  the  instances  he  gives  do  not  appear  to  me  adapted 
to  prove  his  proposition,  that  crustification  may  be  produced  by 
other  causes  than  that  which  I  have  assigned. 

The  banded  structure  of  agates,  so  far  as  I  have  had  opportunity 
to  study  it,  is  a  genuine  crustification.  It  exhibits  incrusted  nuclei, 
stalactites,  and  other  formations  characteristic  of  deposition  in  an 
open  space,  quite  independently  of  the  question  whether  changes  in 
concentration  or  rapidity  of  circulation  or  in  the  substances  contained 
in  the  solution  were  the  occasion  of  precipitation.  In  like  manner 
the  precipitate  formed  upon  a  piece  of  iron  immersed  in  a  solution 
of  copper  sulphate  is  a  genuine  crust,  the  iron  serving  as  the  cause 
of  the  precipitation ;  and  the  circumstances  of  such  a  precipitation 
in  a  space  filled  with  solution,  though  the  process  take  place  above 
ground,  present  some  analogies  with  underground  conditions. 

A  party  of  mine-thieves  once  entered  by  night  an  old  and  exten- 
sive mine  in  Transylvania  for  the  purpose  of  blasting  off  and  car- 
rying away  an  exposed  mass  of  gold-ore.  The  shot  opened  a  hole 
into  an  old  working  (coranda,  in  the  Roumanian  language),  and  one 
of  the  miners  crawled  through.  The  immensity  of  the  space  in 
which  he  found  himself  astonished  him  greatly,  but  his  exclama- 
tions of  wonder  were  cut  short  by  the  crowing  of  a  cock,  which  re- 
vealed to  him  that  he  stood  under  the  night  sky,  in  a  great  surface- 
coranda  or  open  quarry,  which  covered  the  whole  area  of  the  mine. 
Under  some  circumstances,  therefore,  it  is  clear  that  underground 
and  above-ground  are  not  so  very  far  apart ! 

A  mineral  solution  standing  in  a  laboratory-beaker,  exposed  to 
the  air,  may  practically  represent,  from  our  standpoint,  a  subterra- 
nean space,  the  lower  part  of  which  is  filled  with  liquid  and  the 
upper  part  with  gas,  as  I  conceived  it  on  p.  22  of  my  paper. 

Mr.  Becker  doubtless  means,  by  the  examples  he  cites,  to  argue 
that  the  banded  structure  may  originate  also  through  replacement 
of  the  idiogenites  by  xeuogenites.  This  may  be  true,  but  his  in- 
stances do  not  support  the  hypothesis ;  for  the  pseudomorphosis  of 
galena  after  caltite  is  not  a  replacement  of  limestone  by  galena. 
Moreover,  not  every  "  banded  structure  "  is  a  crustification. 

Mr.  Becker  names  two  sorts  of  indications  of  replacement,  namely, 


THE   GENESIS   OF   ORE-DEPOSITS.  231 

crystalline  pseudomorphism  and  the  irregular  enlargement  of  fis- 
sures in  the  replaced  mass.  I  beg  to  say,  that  on  pp.  14  and  15  of 
my  paper,  I  have  mentioned  several  other  signs,  such  as  the  reten- 
tion of  the  structure  of  the  original  mass ;  the  transformation  of 
fossils  into  ore;  the  occurrence  of  remaining  nuclei  of  the  origi- 
nal rock,  etc.,  and  that  I  also  suppose  a  rnetasomatic  process  to 
have  taken  place,  when  the  evidence  is  merely  negative,  that  is, 
where  indications  of  cavity-formation,  in  other  words,  crustification, 
are  absent.  But  I  have  found  deposits  where  the  indications  of  both 
processes  occur  side  by  side,  as,  for  instance,  at  Rodna,  in  Transyl- 
vania. It  was  at  this  place  that  I  had  the  opportunity,  thirty  years 
ago,  to  demonstrate  the  metasomatic  origin  of  an  ore-deposit.  Since 
that  time,  however,  I  have  never  visited  the  locality,  and  have  re- 
ceived only  superficial  data  concerning  further  developments.  Out- 
side of  calamine-deposits,  I  have  not  encountered  in  my  later  explo- 
rations any  cases  of  metasomatic  formation ;  and  I  have  been  led  to 
attach  ever-increasing  importance  to  the  deposits  formed  in  open 
spaces,  the  list  of  which,  as  known  to  me,  has  been  continually  grow- 
ing, while  their  definite  characteristics  have  become  more  and  more 
unmistakably  clear.  Any  difference  of  opinion  which  has  arisen, 
as  a  consequence,  between  my  American  colleagues  and  myself,  must 
be  left  to  the  judgment  of  investigators  who  are  equally  familiar 
with  both  classes  of  ore-deposits. 

My  statement,  "  It  is  difficult  to  believe  that  raetasomatic  pro- 
cesses could  produce  such  pronounced  ore-shoots  as  those  described 
at  Leadville,"  must  be  explained  from  the  standpoint  I  have 
taken  as  to  the  origin  of  cavities  in  a  soluble  rock.  On  p.  19  of 
my  paper,  I  have  shown  that,  before  the  origin  of  the  cavity, 
the  rock-pores  or  interstices  are  filled  with  saturated  solutions, 
and  that  a  line  of  maximum  flow  must  be  subsequently  set  up  be- 
tween the  point  of  entrance  and  some  point  of  minimum  resistance, 
along  which  line  solutions  not  yet  saturated,  finding  access  to  the 
rock,  may  ultimately  dissolve  out  open  channels  or  cavities.  These 
will  then  possess  a  shape  extended  in  one  general  direction,  such  as 
we  encounter  almost  always  in  ore-deposits  in  soluble  rocks.  The 
Leadville  mining  engineers  have  established  such  a  form  for  the 
Leadville  deposits ;  and  Mr.  Becker  has  also  found  it  in  the  quick- 
silver-deposits studied  by  him.  If  I  have  correctly  conceived  the 
formation  of  these  ore-shoots,  they  should  show  some  indications  of 
free  cavity-formation,  even  when  they  have  been  produced  in  part 
by  the  replacement  of  the  original  rock. 


232  THE   GENESIS   OF   ORE-DEPOSITS. 

Finally,  as  regards  the  Eureka  deposits,  I  seem  to  have  been  mis- 
understood. I  did  not  assert  that  the  spaces  originally  occupied  by 
the  Eureka  ore-deposits  had  been  formed  by  surface-waters.  I 
merely  said  (in  accordance  with  Mr.  J.  S.  Curtis)  that  this  was  the 
case  with  the  caves,  which  accompany  the  ores  altered  and  rede- 
posited  by  the  action  of  surface-waters. 

Mr.  F.  M.  F.  Cazin  has  called  attention  to  an  American  example, 
furnished  by  the  Vermont  copper-mine,  in  which  graphite  (or  or- 
ganic matter,  the  remains  of  which  are  now  represented  by  graphite), 
may  have  reduced  the  ore-bearing  solutions.  Mr.  Cazin  cites  the 
fossil  palms  converted  into  copper-glance,  in  the  Trias  of  Mexico,  as 
proof  that  the  copper  was  originally  dissolved  in  the  Triassic  ocean, 
though  perhaps  in  too  small  a  proportion  to  injure  animal  life. 
With  regard  to  that  I  must  observe  that  these  palms  probably  occur 
in  a  fresh-water  basin,  from  which  the  character  of  the  ocean  of  the 
period  cannot  be  inferred ;  nor,  vice  versa,  can  the  traces  of  copper 
found  in  corals  be  adduced  as  indicating  the  probable  presence  of 
copper  in  such  a  basin. 

R.  W.  RAYMOND,  New  York  City  :  The  labor  and  pleasure  of 
translating  Prof.  Posepny's  contributions  having  fallen  to  me,  I 
have  taken  special  interest  in  the  discussion  which  they  have  elicited  ; 
and  I  venture  to  believe  that  an  attempt  on  my  part  to  summarize 
the  results  thus  far  attained  may  be  useful  as  a  help  to  the  further 
discussion  which  I  trust  will  ensue,  and  will  not  be  deemed  an  arro- 
gant assumption  of  the  position  of  a  judge,  which  is  as  far  from  my 
intention  as  it  is  beyond  my  capacity. 

No  amount  of  latitude  in  such  a  discussion  is  reprehensible,  if  it 
elicits  new  facts ;  for  the  accumulation  of  accurate  data  is  really  more 
important  than  the  mere  iteration  of  argument,  and  a  new  fact,  how- 
ever remotely  collateral  in  its  bearing,  may  turn  out  to  be  of  inesti- 
mable value.  In  this  connection,  however,  it  should  be  noted  that 
the  fact  is  valuable  in  proportion  as  it  is  not  merely  the  expression 
of  an  opinion.  When  we  are  told  by  some  authority  that  he  "  found 
unmistakable  evidences  "  of  this  or  that,  we  are  simply  asked  to  ac- 
cept his  conclusion,  which  might  or  might  not  have  been  our  own 
upon  the  same  phenomena ;  and  the  weight  we  give  to  the  fact  of 
his  opinion  as  indicative  of  the  real  facts  behind  it,  which  are  what 
we  want,  depends  upon  our  confidence  in  him,  not  only  as  an  obr 
server,  but  also  as  a  reasoner.  In  my  judgment  we  should  be  grate- 
ful to  Prof.  Posepny  for  the  emphasis  he  has  laid,  not  only  in  this 
paper  but  in  many  preceding  publications,  upon  the  supreme  impor- 


THE   GENESIS   OF   ORE-DEPOSITS.  233 

tance  of  what  he  has  called  rein  objective  Darstellungen,  a  phrase 
which  I  have  weakened  in  ray  translations  by  rendering  it  "accu- 
rate descriptions,"  in  the  fear  that  the  term  "objective,"  used  in  that 
sense,  would  be  misleading.  In  this  connection  I  may  remark,  that 
when  the  admirable  paper  of  Prof.  Posepny  was  sent  to  me,  it  bore  a 
title  which  would  have  been,  literally  translated,  "Subjective  Views 
on  the  Genesis  of  Ore-Deposits,"  the  author  meaning  thereby  to  indi- 
cate modestly  that  he  offered  his  paper  only  as  an  expression  of  the 
opinions  to  which  he  had  been  led  by  his  own  studies,  and  not  as  a 
statement  of  the  settled  results  of  science.  I  took  the  liberty  of 
objecting  to  this  title,  on  the  ground  that  "subjective"  views  might 
be  construed  as  opinions  simply  "evolved  from  the  inner  con- 
sciousness,'7 without  any  foundation  whatever  in  observed  facts  ;  and 
as  a  result  of  this  correspondence,  Prof.  Posepny  permitted  the  use  of 
the  simpler  title,  accompanied  with  such  introductory  explanations 
as  would  relieve  him  from  the  imputation  of  dogmatism. 

Accepting,  however,  his  use  of  "subjective"  and  "objective"  as 
connoting  statements  respectively  affected  or  unaffected  by  in- 
dividual opinion,  we  cannot  but  appreciate  and  share  his  desire 
for  "  purely  objective "  reports  of  observed  facts  in  the  field  of 
his  studies.  And,  since  it  is  extremely  difficult  to  convey  an 
"objective"  description  in  writing,  the  superiority  of  a  careful 
drawing  (not  an  "  ideal  "  diagram,  though  that  has  its  uses,  and  is 
often  a  better  vehicle  of  description  than  words)  is  clear.  Prof. 
Posepny  has  practiced  his  own  doctrine  by  illustrating  his  paper 
with  numerous  drawings,  and,  I  may  add,  he  has  unconsciously  en- 
forced that  doctrine  by  betraying  his  own  doubts  and  difficulties  in 
the  interpretation  of  mere  verbal  and  partly  "subjective"  descrip- 
tions, given  by  other  authors. 

The  misunderstandings  thus  occasioned  may  be  left  to  settle  them- 
selves through  mutual  explanations,  such  as  have  been  made,  more 
or  less  fully,  in  the  course  of  this  discussion.  It  need  only  be  added 
here  that  Prof.  Posepny's  conscientious  and  frank  declarations  as  to 
the  limits  of  his  personal  observation  and  his  careful  references  to 
all  authorities  cited, constitute  a  safeguard  against  error,  a  full  guide 
to  further  investigation  and  a  model  for  our  imitation. 

But  the  chief  questions  of  interest  to  us,  I  think,  are  these :  What 
are  the  characteristic  and  valuable  contributions  made  by  this 
paper  to  the  theory  of  the  genesis  of  ore-deposits  ?  and,  What  are 
the  definite  issues  on  which  Prof.  Posepny's  views  differ  from  those 
of  other  observers,  as  the  latter  have  been  represented  in  this  dis- 
cussion ? 


234  THE   GENESIS   OF   ORE-DEPOSITS. 

Under  the  first  head  I  think  we  may  regard  as  pre-eminent  the 
masterly  exposition  of  the  subject  of  underground  circulation  and 
the  distinction  established  between  the  vadose  and  the  deep  circula- 
tion, the  former  actuated  .mainly  by  gravity  and  conditioned  upon 
the  relative  position  of  the  surface-outflow,  the  latter  complicated  by 
the  effects  of  capillarity  and  pressure  due  to  heat.  This  distinction 
supersedes  the  vague  terms  " ascending"  and  " descending,"  though 
the  author  has  employed  these  terms,  in  accordance  with  popular 
usage,  and  has  thereby  incurred  some  unnecessary  criticism.  For  it 
is  really  not  of  the  slightest  importance  to  the  general  theory  of  this 
subject  whether  a  given  mineral  solution  was  moving  horizontally 
or  up  and  down  when  it  produced  a  given  precipitate.  The  only 
significant  question  is  whether  it  was  on  the  way  up  or  down;  that 
is,  whether  it  belonged  to  the  one  or  to  the  other  branch  of  the  un- 
derground circulation.  The  third  view,  namely,  that  such  a  solution 
might  belong  neither  to  the  vadose  downward  circulation  nor  to  the 
deep  upward  circulation,  but  to  a  "  lateral  secretion,"  Prof.  Posepny 
practically  declares  to  be  inconceivable.  As  I  understand  his  argu- 
ment (or  rather,  perhaps,  as  I  would  state  my  own  view,  which  I 
think  to  be  in  substantial  accordance  with  his),  it  may  be  expressed  as 
follows : 

1.  The  aqueous  solutions  underground  must  be  conceived  either 
(a)  as  moving  on  a  general  downward  course,  as  parts  of  the  vadose 
circulation,  above   ground-water   level,  or  (6)  as    penetrating  still 
deeper   into  the  rocks  below  drainage-level  (the  barysphere),  or  (c) 
as  rising  from  those  depths  under  pressure,  overcoming  gravity,  to- 
wards or  to  the  surface;  or  (d)  as  standing  (held  by  capillarity  or 
otherwise)  in  rocks,  whether  above  or  below  the  drainage-level,  and 
not  participating  in  the  circulation  at  all. 

2.  Concerning  the  condition  (a),  which  is  most  open  to  our  obser- 
servation  we  know  a  great  deal.     We  know,  for  instance,  from  an 
overwhelming   number  of  observations,  that  the  solutions  of  the 
vadose  circulation  are  oxidizing,  and  that  (apart  from  the,  probably 
rare,  re-formation  of  sulphides  by  the  action  of  organic  matter)  they 
do  not  precipitate  sulphides,  but,  on  the  contrary,  attack  and  decom- 
pose them. 

3.  Concerning  (6),  we  know  nothing  by  direct  observation,  but  are 
forced  to  believe,  and  justified  (by  Daubree's  experiments,  etc.)  in  be-, 
lieving,  that  such  a  movement  actually  takes  place. 

4.  Concerning  (c),  we  have  the  evidence  derived  from  hot  springs, 
etc.,  which  has  convinced  all  observers  that  there  is  in  fact  such  an 
ascending  circulation,  whatever  may  be  their  conclusions  as  to  the 


THE   GENESIS   OF   ORE-DEPOSITS.  235 

depth  of  its  origin  or  the  degree  of  its  agency  in  forming  mineral 
deposits.  The  ascension-theory  postulates  concerning  it  only  that  it 
comes  from  depths  below  drainage-level,  and  is  not  moved  merely 
by  siphon-action,  ultimately  due  to  gravity. 

5.  Concerning  (d),  it  may  be  said  that  solutions  thus  held  without 
participation  in  the  general  circulation,  while  they  may  affect  in- 
ternal changes  in  the  rocks  they  occupy,  cannot  begin,  until  they  be- 
gin to  move,  a  process  of  redistributing  and  concentrating  by  pre- 
cipitation elsewhere  the  substances  they  hold  in  solution. 

6.  Moreover,  solutions  in  the  condition  (cZ),  though  not  partici- 
pating in  the  general  circulation,  must  have  reached  their  loeus  by 
means  of  that  circulation.     They  musC  be  conceived  as  having  been 
a  part  either  of  the  downward  or  of  the  upward  branch,  or,  in  other 
words,  as  arrested  portions  of  the  circulation.' 

7.  Whenever  they  begin  to  move,  they  must  join  one  or  the  other 
branch  of  the  circulation  ;  and  the  deposits  they  may  make  must  be 
the  result  of  the  laws  of  that  branch,  operating  upon  the  nature  of 
the  solutions,  this  in  turn  being  partly  dependent  upon  their  original 
source. 

8.  There  is,  therefore,  no  room  for  a  hypothesis  of  ore-concentra- 
tion and  deposit  in  bodies  of  considerable  size  by  "secretion,"  inde- 
pendent of  circulation,  or  for  a  cycle  of  circulation,  complete  in  it- 
self, yet  not  participating  in  the  general  phenomena  described.     For 
continuous  currents  must  come  from  somewhere  and  go  somewhere; 
and  neither  inflow  nor  outlet  is  provided,  except  by  the  conditions  of 
the  general  underground  circulation,  as  described. 

9.  From  this  standpoint  it  is  clear  that  the  source  of  the  sub- 
stances carried  in  solution  by  a  current  must  lie  somewhere  in  the 
path  which  that  current  has  traversed.     If  the  theory  of  lateral  se- 
cretion means  no  more  than  the  assertion  that  the  mineral  solutions 
which  have  precipitated  ore  in  a  given  fissure  or  space  have  traversed 
and  leached  some  rock  before  entering  that  space  and  that  this  rock 
adjoined  or  lay  in  "  reasonable  proximity  "  to  the  space  of  deposi- 
tion, it  would  mean,  as  to  the  first  proposition,  nothing  that  anybody 
denies ;  while,  as  to  the  second  proposition,  it  would  be  a  somewhat 
vague  assertion,  requiring  definite  proof  in  each  case,  and  not  en- 
titled to  the  dignity  of  a  general  theory. 

10.  But   the  theory  of  lateral  secretion,  however  it    may  have 
melted  away  under  the  fire  of  criticism,  originally  claimed  more  than 
this.     Prof.  Sandberger  says  :* 

*   Untersuchungen  ilber  Erzgange,  von  Fridolin   Sandberger.     Wiesbaden,  1882, 
Erstes  Heft.  pp.  3,  4. 


236  THE   GENESIS   OF   ORE-DEPOSITS. 

"The  so-called  descension-theory  of  Werner  is  purely  neptunic,  and  regards 
veins  as  exclusively  filled  from  above  downwards  by  the  deposition  of  ores  from 
liquids,  without  answering  the  question,  whence  these  liquids  derived  their  me- 
tallic contents.  The  descension-theory  remains  good  to-day  for  all  cases  where,  in 
higher-lying  rocks,  those  substances  can  be  with  certainty  traced,  which  have  col- 
lected as  ore-deposits  in  cavities  and  fissures  in  lower-lying  rocks,  not  originally 
containing  them.  If  the  ores  are  accumulated  in  fissures,  they  possess  all  the 
characters  of  fissure- veins.  So  far  as  my  knowledge  of  ore-deposits  goes,  the  filling 
of  fissures  by  ores  which  can  be  clearly  proved  to  have  filtered  in  from  above  is  not 
very  frequent;  but  such  fillings  of  irregular  cavities  are  common." 

After  mentioning  as  an  excellent  instance  the  lead-  and  zinc-de- 
posits of  Raibl  (which  Prof.  Posepny  has  discussed  with  very  differ- 
ent conclusions),  and  declaring  that  he  is  at  present  concerned 
specially,  not  with  such  deposits,  but  with  true  fissure-veins,  Prof. 
Sandberger  proceeds  to- state  as  follows  the  ascension-theory,  which 
he  says,  "  still  counts  many  adherents,"  and  which  he  proposes  to 
controvert : 

"  The  ascension-theory  assumes  in  all  cases  that  the  ores  occurring  in  a  vein-fis- 
sure were  derived  either  not  at  all,  or  only  in  part,  from  the  immediately  adjacent 
country- rock  (aus  dem  unmittelbaren  Nebengestein),  but  on  the  contrary,  from  greater 
depths,  and  have  been  introduced  into  the  fissures  either  by  ascending  mineral 
springs  or  by  sublimation.  The  substances  deposited  in  the  veins  should  therefore 
be  different  from  those  of  the  adjacent  rock,  and  should  only  occur  in  the  latter  as 
lateral  impregnations  from  the  fissures." 

Confining  himself  to  the  supposed  agency  of  ascending  mineral 
springs,  the  author  asserts  that  such  springs  would  not,  and  in  fact,' 
do  not,  deposit  minerals  in  their  channels,  and  discusses  at  some 
length  the  case  of  Sulphur  Bank  in  California,  which  he  declares  to 
be  the  only  instance  apparently  contradicting  his  view.  He  argues 
against  the  conclusions  drawn  by  others  from  this  instance,  and  con- 
cludes as  follows  (p.  17) : 

"  If,  then,  the  only  region  in  which  it  has  been  deemed  possible  to  assume  the 
filling  of  vein-fissures  by  ascending  mineral  springs  as  a  process  now  going  on, 
furnishes  no  trustworthy  proofs  for  this  assumption,  what  remains  ?  In  my  opinion, 
only  the  leaching  of  the  country-rock  which  bounds  the  fissures  by  seepage-waters 
which  have  penetrated  it,  and  which  deposit  the  dissolved  materials  as  ores  and 
gangue  in  the  fissures  of  the  same  (or,  in  exceptional  cases,  the  nearest  neighbor- 
ing) rock.*  This  is  the  so-called  lateral-secretion  theory  in  its  most  prosaic  form  ; 
and  it  is  this  to  which  I  have  been  so  distinctly  led  by  many  years  of  observation 
and  investigation  that  I  am  forced  to  consider  it  applicable  to  most  ore-veins." 


*  "  Nach  meiner  Ausicht  nur  Auslaugung  des  die  Spalten  begranzenden  Nebenge- 
steins  durch  Sickerwasser,  welche  dasselbe  durchdrungen  haben,  und  die  gelosten 
Stoffe  als  Erze  und  Gangarten  in  den  Spalten  des  gleichen  oder  ausnahrasweise 
auch  in  solchen  des  nachsten  Nachbargesteins." 


THE   GENESIS   OP   ORE-DEPOSITS.  237 

11.  It  is  clear  that  this  theory  contemplates  the  exclusion  of  the 
agency  of  waters  rising  from  below  drainage-level.     That  there  are 
such  waters,  is  an  admitted  fact;  and  it  must  be  also  admitted  that 
they  are  under  pressure  great  enough  to  overcome  gravity  and  fric- 
tion.    All  fissures  accessible  to  such  waters,  they  must  necessarily 
occupy ;  and  it  seems  to  follow  inevitably  that  all  fissures  extending 
below  drainage-level  must  be  filled,  up  to  that  level  at  least,  with 
waters  either  in  actual  circulation  on  their  way  upward,  or  tempo- 
rarily arrested  and  confined.     "  Seepage"  into  such  spaces  is  incon- 
ceivable. 

12.  On  the  other  hand,  currents  under  pressure  would  necessarily 
penetrate  into  the  pores  and  interstices  of  the  rocks  bounding  their 
main  channels,  and   the  deposit  in  such   rocks  of  minerals  carried 
from  the  fissures  is  more  probable  a  priori  than  the  deposit,  in  the 
fissures,  of  minerals  dissolved  from  the  adjoining  rocks.     The  oppo- 
site would  be  true  if  the  fissures  did  not  contain  water,  a  condition 
which  can  only  be  assumed  when  there  is  a  lower  outlet,  that  is  to 
say,  only  in  the  zone  of  vadose  circulation. 

13.  The  advocates  of  lateral  secretion  must  state,  at  least,  their 
conception  of  the  way  in  which  "seepage"  can  take  place  from  a 
porous  solid  holding  water  into  an  adjoining  space  also  filled  with 
water,  and  under  higher  pressure.     That  practically  no  interchange 
between  the  two  will  take  place,  even  if  the  pressures  are  equal,  is 
shown   by  the  occurrence  of  fresh-water  springs  along  our  coast, 
separated  by  a  few  feet  of  sand  only  from  the  salt  waters  of  the  sea. 
It  is  often  popularly  supposed  that  the  sea- water  has  been  deprived 
of  its  salt  by  "  filtration  "  through  the  sands ;  but  the  real  fact  is, 
that  the  mass  of  the  sea  bars  the  path  of  a  circulation  which  would 
carry  the  spring- water  into  it,  and  the  spring  seeks  another  way  to 
the  surface,  where  it  emerges  perfectly  fresh.     The  intervening  sands 
are  doubtless  filled  with  brackish  water,  but  this  takes  no   part  in 
the  circulation,  and  therefore  carries  no  salt  into  the  channel  of  the 
spring.     If  the  Atlantic  Ocean  cannot  "  seep  "  salt  into  a  spring  of 
fresh  water,  how  could  a  rock,  not  included  in  the  path  of  a  con- 
tinuous circulation,  impregnate  any  portion  of  that  path  by  its  "see- 
page?" 

14.  Again,  it  is  conceivable  that   gash-veins,  and   other   spaces 
wholly  within  a  given  rock-mass,  may   receive  concentrations  of 
mineral  by  "  seepage,"  though  even  in  this  case,  if  the  process  is  to 
result  in  considerable  accumulations  of  mineral,  it  must  be  a  long- 
continued  one,  supported  by  an  inflow  and  outflow  ;  in  other  words, 


238  THE   GENESIS   OF   ORE- DEPOSITS. 

it  must  be  a  part  of  a  general  ascending  or  descending  circulation. 
And  since  the  ascending  circulation  involves  a  pressure  from  the  fis- 
sure towards  the  wall-rock,  that  is,  in  the  wrong  direction  for  "seep- 
age," it  follows  that,  except  in  the  vadose  region,  and  apart  from 
highly  exceptional  conditions,  the  products  of  the  leaching  of  any 
given  rock-mass  are  not  likely  to  be  found  predominantly  in  adjoin- 
ing fissures. 

15.  The  theory  of  lateral  secretion,  therefore,  is  essentially  con- 
fined to  the  region  of  the  vadose  circulation  ;  and  those  who  would 
apply  it  to  the  origin  of  deposits  containing  sulphides  must  be  pre- 
pared to  maintain  that  those  sulphides  have  been  deposited  from 
solutions   moving  downwards  or   laterally,  under  the   influence  of 
gravity,  in  other  words,  surface-waters.     Prof.  Sandberger  does  not 
hesitate  to  accept  this  alternative,  although   he  does  not  perceive, 
apparently,  how  it  confines  the  sphere  of  his  theory.     According  to 
his  view,  the  metals  are  disseminated  in  the  country-rocks  and  sili- 
cates, and  these  rocks  contain  also  sulphate  of  soda,  and  other  soluble 
alkaline  sulphates,  as  well  as  chloride  of  sodium,  all  of  which,  he 
supposes,  are  converted  by  organic  matter  into  alkaline  sulphides, 
which  transform  the  metallic  silicates  into  metallic  sulphides. 

16.  But  this  explanation  encounters  two  serious  difficulties.     In 
the  first  place,  it  is  opposed  to  the  overwhelming  evidence  that  the 
downward  circulation  does  not  characteristically  deposit  sulphides, 
but  attacks  them  ;  that  it  does  not  characteristically  contain  alkaline 
sulphides,  but  alkaline  carbonates  and  free  carbonic  acid  and  oxygen. 
In  the  second  place,  the  explanation   breaks    down  in  the  presence 
of  fissures  filled  with  sulphides,  extending  far  below  any  present 
or  conceivable  past  drainage-level.     The  sulphide   ore-deposits    in 
such  fissures,  at  the  greatest  depths  attained   by  mining,  show  no 
structural  differences  or  other  indications  of  a  different  origin,  as 
compared  with  sulphides  in  the  levels  above.     There  is  a  change  at 
water-level,  but  it  is  notoriously  a  change  from  oxidation  above,  to 
absence  of  oxidation  below,  that  level. 

17.  The  lateral -secretion  theory,  therefore,  so  far  as  it  is  true  at 
all,  is  no  more  than  a  subordinate  division  of  the  theory  of  the  for- 
mation of  deposits  in  open  spaces  above  drainage-level ;    and   even 
here,  it  is  neither  necessary   nor  plausible,  as  the   explanation   of 
deposits  which  continue  downwards,  and  must  be  referred,  as  regards 
their  lower  portions,  to  a  deep  source.     Such  deposits'may  have  been 
altered  in  character  and  even  in  form,  in  the  vadose  region ;   they 
probably  originated  in  the  deep  region. 


THE   GENESIS   OF   ORE-DEPOSITS.  239 

18.  On  the  other  hand,  the  hypothesis  of  ascending  waters  as  the 
vehicle  of  solution  and  deposition  does  not  exclude  the  idea  of  the 
leaching  of  any  rock  traversed  by  such  waters.      It  indeed  assumes 
such  a  leaching  as  having  taken  place  somewhere.     But,  as  opposed 
to  the  theory  of  lateral  secretion  (modified  to  lateral  circulation)  it 
assumes  the  rock  immediately  adjoining  a  vein-fissure  (when  the  fis- 
sure continues  deeper)  to  be  the  least  likely,  not  the  most  likely, 
source  of  the  metallic  ores.     And  on  this  point  it  appeals  to  the  phe- 
nomena of  crustification.       Nothing  is  plainer  than   the  evidence 
afforded  by  the  successive  crystalline  crusts  of  an  amethyst  geode,  for 
instance,  that  the  deposition  took  place  first  upon  the  walls  of  the 
cavity,  afterwards  upon  the  crust  thus  formed,  and  so  on  towards 
the  central  druse.     The  very  first  deposit  evidently  covered  the  wall 
with  an  impermeable  layer;   and  the  material   for  all  succeeding 
deposits  must  have  come  (as  the  sections  of  many  geodes  show  visi- 
bly that  it  did  come),  through  a  passage  from  without  the  mass  of 
the  geode.     In   like  manner,  the  crustified  filling  of  a  fissure-vein 
cannot  well  have  come  from  the  walls  of  the  vein  at  the  place  where 
the  first  crust  deposited  would  necessarily  close  those  walls.     The 
crusts  have  been  deposited  from  a  solution  between  them.     The  cen- 
tral druse  was  not  first  formed,  and  then  pushed  out  by  successive 
deposits  behind  it,  as  the  bark  of  a  tree  is  thickened.     The  solution 
depositing  the  crystals  in  successive  crusts  must  therefore  have  been 
part  of  a  current ;  and  its  entrance  and  exit  can  scarcely  be  sought,  as 
a  rule,  in  the  walls  it  has  crusted.     A  side-fissure,  entering  through 
either  wall,  is,  of  course,  not  impossible  or   uncommon.       But  it 
cannot  be  assumed  to  exist,  without  proof.     And  when  such  a  thing 
is  actually  found,  its  effect  upon  the  vein  is  so  marked  as  to  raise  a 
strong  presumption  that  the  normal  source  of  the  vein-solutions  was 
not  in  that  direction. 

19.  Prof.  Posepny  has  laid  much  emphasis  upon  crustifieation,  as 
he  has  defined  that  term.     I  think  he  is  right  in  so  doing ;  and  I 
may  remark  incidentally  that  his  use  of  new  special  terms  (which 
has  been  objected  to  by  some),  is  justified,  in  this  case,  as  in  other 
cases,  by  the  greater  precision  of  thought  thereby  secured.     The  dis- 
advantage of  a  preference  for  ordinary  and  familiar  words,  when 
such  words  may  have  many  meanings,  is  illustrated  by  the  manner 
in  which  Prof.  Posepny,  on  the  one  hand,  and  his  critics,  on  the 
other,  have  been  misled  by  the  ambiguity  of  "  banded  structure." 
He  interprets  "  banded  structure,"  or  equivalent  expressions,  in  some 
of  the  authorities  he  cites,  as  meaning  crustification,  and  they  say 


240  THE   GENESIS   OF   ORE-DEPOSITS. 

that  banded  structure  may  arise  in  several  ways,  intimating  thereby 
that  crustification  is  not  a  sure  proof  of  deposition  upon  cavity-walls. 
The  verbal  misconception  being  corrected,  it  seems  to  me  that  there 
is  no  difference  between  the  parties  on  this  head. 

20.  The  assertion  that  a  current  is  necessary  for  the  deposition  of 
such  crustified  accumulations  is  not  to  be  construed  as  excluding 
variations  in  velocity,  or  occasional  stoppages  and  intermissions.  The 
objection  of  Prof.. Sand berger,  that  mineral  springs  do  not,  as  a  fact, 
deposit  solid  substances  in  their  channels,  seems  to  be  based  upon  the 
conception  of  such  springs  as  ascending  with  unvaried  velocity,  as 
if  through  pipes  of  uniform  diameter.  Even  pipes,  as  Professor 
Posepny  reminds  us,  have  been  known  to  receive  interior  incrusta- 
tions ;  but  the  probability  of  such  deposfts  is  much  increased 
when  the  effects  of  variations  in  the  nature  and  size  of  the  channel 
are  taken  into  account.  Mutatis  mutandis,  the  analogy  of  the  de- 
position of  sediments  by  a  running  stream  is  available  here.  As 
sands  and  clays,  carried  in  suspension  where  the  current  is  most 
rapid,  are  dropped  where  it  is  checked  through  widening  of  the 
channel,  or  from  other  causes,  so  the  deposits  of  a  mineral  circula- 
tion will  naturally  be  greatest  where  the  movement  is  slowest,  or  is 
even  temporarily  arrested  altogether  ;  and  they  will  be  reduced  to  a 
minimum,  other  things  being  equal,  where  the  current  is  most  rapid. 
The  phenomenon  of  distinct  crustification,  in  fact,  requires  the  hy- 
pothesis of  a  relative  quiescence  of  the  menstruum.  And  instances 
are  not  wanting  underground  in  which  the  widening  of  the  vein- 
fissures,  or  the  change  to  a  flatter  dip,  has  apparently  favored  the 
deposition  of  ore.*  The  aseension-theory  does  not  exclude  these 
obvious  considerations.  All  it  asserts  is,  that  the  portion  of  solution 
entering  a  given  space,  and  depositing  therein  a  precipitate,  must 
thereafter  escape  and  give  place  to  another  portion  of  solution,  if  the 
process  is  to  be  repeated  ;  and  that,  with  regard  to  deposits  of  sul- 
phides, formed  below  drainage-level,  the  only  escape  is  ultimately 
upward.  But  the  phenomena  of  crustification  in  veins  afford,  in 

*  On  the  other  hand,  increased  width  of  "  vein-matter  "  has  often  been  due  to  a 
splitting  of  the  fissure,  and  the  enclosure  of  fragments  of  country -rock,  which  is 
afterwards  more  or  less  transformed  into  gangue,  or  remains  as  horses  in  the  vein. 
Or,  such  increased  width  may  be  (as  in  the  Cornwall  tin-mines)  the  result  of  a 
mineralization  of  the  country-rock  beyond  the  limits  of  the  original  fissure,  pro- 
ducing a  mass  of  altered  rock  impregnated  with  ore  (the  Zinnzwitter  of  the  Ger- 
mans). In  such  cases,  while  the  aggregate  of  mineral  deposited  is  doubtless  much 
greater  than  it  would  have  been  had  the  solution  passed  through  the  narrow  fissure 
only,  the  richness  of  the  material  is  reduced  by  the  admixture  of  gangue  and  rock. 


THE   GENESIS   OF   ORE-DEPOSITS.  241 

my  judgment,  another  argument  against  the  theory  of  lateral  secre- 
tion. Namely,  it  is  well  known  that  the  crustification,  even  in  typi- 
cal fissure-veins,  is  not  everywhere  distinct.  If  it  can  be  observed, 
with  its  characteristic  central  druse,  in  one  part  of  a  vein,  it  is  held 
(properly,  I  think)  to  be  (in  the  absence  of  evidence  to  the  contrary) 
a  proof  that  the  similar  ores  of  other  parts  of  the  vein  have  been 
similarly  deposited.  The  absence  of  crustification  in  some  places 
may  be  explained,  on  the  ascension-theory,  by  the  varying  speed  of 
the  current,  and  the  varying  nature  and  dip  of  the  walls,  as  affecting 
the  deposition  of  adherent  crystalline  crusts.  The  chemical  or  phy- 
sical causes  inducing  precipitation  may  simply  produce  a  suspended 
precipitate,  to  be  subsequently  deposited  as  a  sediment.  But  if  lateral 
secretion  has  produced  crustification,  such  as  is  observed  in  fissure- 
veins  (as  I  think,  with  Professor  Posepny,  that  it  has  not)  then  that 
structure,  it  seems  to  me,  should  be  more  uniformly  distinct  in 
such  veins  than  it  is.  For  the  conception  of  lateral  secretion  into  a 
fissure  excludes  the  conception  of  a  current  under  higher  pressure, 
already  occupying  that  fissure;  and  the  local  interference  of  such  a 
current  with  the  quiet  process  of  crystallization  is  therefore  out  of 
the  question. 

21.  The  comparatively  small  amount  of  mineral  matter  contained 
in   the  ascending  springs  of  the  deep  circulation,  originating  below 
drainage-level,  is  to  my  mind  some  indication  that  they  have  already 
deposited   somewhere   the   larger  part  of  the  substances  they  have 
held  in  solution.     They  are  never  saturated  solutions.     As  we  find 
them,  they  contain  what  we  may  suppose  to  be  only  remaining  traces 
of  the  metallic  constituents  which  they  may  (we  may  almost  say 
must)  have  carried  at  greater  depths,  temperatures,  and  pressures.  Is 
not  the  presence  of  these   minute  remainders  really  an  evidence  of 
the  larger  amounts  once  present,  and  therefore  of  a  precipitation  en 
route?   In  connection  with  this  question,  the  probable  conditions  of 
the  deep  zone  must  be  borne  in  mind,  such  as,  not  only  the  increased 
solvent  power  of  the  waters  of  that  zone,  but  also  the  probable  slow- 
ness of  their  downward  progress,  which  is  practically  (according  to 
Daubree)  a  seepage,  and  which  must  favor  the  formation  of  saturated 
solutions. 

22.  In  reply  to  this  suggestion,  the  question  may  be  raised,  how 
the  deposition  of  ores,  extending  almost  or  quite  to  the  surface,  is  to 
be  accounted  for,  if  the  solutions  now  encountered  below  drainage- 
level,  are  already  so  nearly  exhausted  as  to  be  capable  of  compara- 
tively little  further  precipitation.     Without  forgetting  that  the  most 

16 


242  THE    GENESIS   OF   ORE-DEPOSITS. 

dilute  solutions  may  still  give  precipitates  under  chemical  or  phys- 
ical changes  of  condition ;  and  that  such  precipitates,  however  in- 
significant, may  attain  a  considerable  aggregate  amount  by  long-con- 
tinued repetition,  I  think  the  more  comprehensive  answer  to  the 
above  question  is  found  in  the  conclusion  to  which  we  are  led  by  the 
ascension- theory,  that  deposits  carrying  metallic  sulphides,  though 
they  reach  the  present  surface,  were  formed  mainly  below  the  influ- 
ence of  the  vadose  circulation,  and  therefore  under  conditions  such 
as  may  now  obtain  at  depths  beyond  our  observation. 

23.  This  suggests  another  point,  to  which  Prof.  Posepny  has  called 
attention,  and  which  was  acutely  recognized  by  Cotta,  many  years 
ago,*  namely,  the  fact  that  speculations  upon  the  relation  between 
the  contents  of  mineral  veins  and  their  depth  are  largely  vitiated  by 
the  vagueness  and  uncertainty  of  the  element  of  depth,  as  estimated 
by  comparison  with  the  present  surface.  In  most  mining  regions 
there  is  unquestionable  evidence  of  great  denudation,  which  has  pro- 
bably removed  from  the  surface  a  larger  mass  than  has  been  pene- 
trated anywhere  by  mining.  It  seems  impossible,  therefore,  to  argue 
as  to  the  continuance  of  ores  "  in  depth,"  meaning  thereby  beyond 
1000  or  2000  feet  from  the  present  surface,  when  that  surface  itself 
may  have  been  10,000  feet  underground  at  the  time  the  ores  were 
deposited.  We  may  imagine  that  the  ascending  waters  in  a  vein 
now  rich  in  metallic  deposits  "from  the  grass-roots  down,"  once 
continued  their  upward  course  to  the  former  surface,  emerging  as 
dilute  solutions;  or  never  reached  that  surface  intact,  but  encoun- 
tering the  vadose  circulation,  became  a  part  of  it;  and,  in  either 
case,  precipitated  less  and  less  metallic  matter  as  they  ascended. 
Conversely,  we  may  reasonably  imagine  that,  if  we  could  retrace  the 
course  of  a  mineral  spring  coming  from  the  deep  zone,  it  might  lead 
us  back  to  the  region  where  it  had  deposited  the  treasure  of  which 
it  now  exhibits,  at  most,  only  faint  remaining  traces.  And  what  we 
might  thus  fairly  imagine  concerning  an  actual  spring  might  be 
equally  true  of  the  channel  of  a  former  spring  now  closed  altogether, 
or  occupied  only,  under  changed  conditions  of  altitude  and  drainage, 
by  the  vadose  circulation — that  is  to  say,  of  a  fissure-vein,  compara- 
tively barren  or  lean  at  the  present  surface.  In  other  words,  the 
present  surface  is  an  arbitrary  section,  cutting  off  the  veins.  Those 
which  it  happens  to  intersect  in  their  richer  portions,  are  naturally 
the  ones  which  are  developed  by  mining.  Those  which  it  shows  to 

*  Die  Lehre  von  den  Erzlagerstatten,  Freiberg,  1858.     Part  I.,  p.  129. 


THE   GENESIS   OF   ORE-DEPOSITS.  243 

be  locally  barren,  are  naturally  not  thus  developed,  unless  local 
experience  supports  the  hope  that  they  will  improve  in  depth. 
Such  a  local  experience  is  doubtless  the  foundation  of  the  maxim 
which  Cornish  miners  have  carried  throughout  the  world,  that  "  a 
fissure-vein  grows  richer  in  depth,"  a  proposition  for  which,  as  a 
general  guide  for  mining  (apart  from  the  effects  of  surface-waters, 
which  may  be  sometimes  impoverishing),  is  without  foundation  in 
experience.  For  although  a  comparatively  barren  fissure  may  be, 
and  has  often  been  shown  to  be,  the  upper  part  of  a  vein  carrying 
rich  ores  below,  there  is  no  general  law  that  it  must  be  so ;  and, 
moreover,  there  is  no  way  of  determing  a  priori  the  depth  of  the 
barren  zone,  measured  from  the  present  surface. 

24.  On  the  other  hand,  while  the  varying  positions  of  the  present 
surface  prevent  generalization  as  to  the  relations  of  ore  to  "  depth/7 
it  is  unquestionably  possible  that  there  may  be,  in  a  given  fissure,  a 
relation  of  that  kind.     The  ascension-theory    neither   asserts    nor 
denies  such  a  supposition.     Mr.  Rickard's  suggestion  that  the  deeper 
zone  must  be  the  region  of  solution,  and  a  higher  zone  the  region  of 
precipitation,  is  speculatively  reasonable  enough;  but  it  amounts  to 
a  proposed  subdivision  of  the  barysphere  into  two  regions;    for  the 
deep  zone  which  Prof.  Posepny  has  called  the  barysphere  includes 
everything  below  our  observation,  and  it  is  in  that  zone  that  both 
solution  and  precipitation  are  supposed  to  have  taken  place  to  form 
the  deposits  of  metallic  sulphides.     In  our  ignorance  of  the  condi- 
tions of  that  unknown  region,  it  is  scarcely  possible  or  necessary  to 
frame  hypotheses  concerning  them.     The  practical  bearing  of  Mr. 
Rickard's  suggestion   lies  in  his  connection  of  it  with  an  alleged 
general  phenomenon  of  the  impoverishment  of  veins  in  depth,  as 
shown  by  experience  in  mining. 

25.  As  to  this  alleged  general  phenomenon,  I  would  say  first,  that 
even  if  it  were  proved,  it  could  hardly  be  ascribed  to  the  cause  sug- 
gested  by   Mr.  Rickard,  namely,  the   predominance  of  solution  in 
lower  zones  and  the  confinement  of  precipitation  to  higher  ones,  be- 
cause the  depths  reached  in  mining  are  not  great  enough  to  warrant 
such  a  deduction,  and  also  because  the  instances  (such  as  Przibram) 
of  rich  ores  continuing  for  great   vertical   distances,  and   down  to 
levels   among  the  deepest  ever  opened   by  mining,  contradict  the 
hypothesis. 

But  it  must  be  confessed  that  there  is  much  evidence  which  seems 
to  corroborate  Mr.  Rickard's  statement  as  to  the  exhaustion  of  mines 
in  depth.  This  evidence  needs,  however,  to  be  carefully  collated 


244  THE   GENESIS   OF   ORE-DEPOSITS. 

and  critically  sifted,  before  it  can  be  accepted  as  the  indication  of  a 
natural  law. 

a.  In  such  an  inquiry  all  cases  must  be  rejected  in  which  oxidized 
surface-ores  have  been  mined  down  to  water-level,  and  the  mine  has 
been  abandoned  by  reason  of  treating  the  refractory  sulphides.     In 
many  such  cases  the  oxidized  ores  are  actually  richer  (e.g.  in  gold) 
by  reason  of  the  alteration  they  have  undergone;  but  this  is  not  per- 
tinent to  the  question  of  original  deposition. 

b.  The  abandonment  of  mines  by  reason  merely  of  the  increased 
cost  of  deep  mining  must  be  also  set  aside  as  affording  no  evidence 
on  this  subject. 

c.  The  fact  that  in  mining  a  bonanza  is  traversed,  and  a  relatively 
barren  zone  occurs  below,  does  not  necessarily  indicate  a  relation  be- 
tween barrenness  and   depth.     The  occurrence  of  a  bonanza   very 
frequently  involves  barrenness  of  the   neighboring  portions  of  the 
vein.     That  this  is  the  case  on  a  horizontal  line  is  abundantly  proved. 
An  instance  in  point  is  furnished  by  the  Bullion  mine  situated  on  the 
Comstock  lode,  between  mines  which  have  produced  many  millions. 
The  expenditure  of  millions  on  the  Bullion   never   produced,  so  far 
as  I  know,  a  ton  of  profitable  ore.     Why  should  not  a  similar  alter- 
nation of  rich  and  barren  places  occur  in   the  vertical  line?     The 
cost  of  exploration   in  depth,  and  particularly  in  sinking,  naturally 
discourages  mine-owners  ;    and   the    abandonment  of  an    operation 
under  such  circumstances  really  proves  nothing. 

d.  In  any  case  of  alleged  impoverishment  of  a  vein  in  depth,  not 
only  the  actual  depth  below  the  present  surface,  but  also  (so  far  as  it 
can  be  estimated)  the  probable  amount  of  denudation  which  the  sur- 
face has  undergone,  should  be  taken  into  account. 

e.  The  nature  of  the  ore  also  may  have  a  distinct   bearing  upon 
this  inquiry.     It  is  my  impression  that  of  the  loose  and  vague  evi- 
dence thus  far  accumulated,  a  large  part  refers  to  gold-ores,  and  par- 
ticularly to  free  gold  in  quartz,  as  "  giving  out  "  in  depth.     I  re- 
member that  in  my  last  conversation  with  the  late  Joshua  E.  Clay- 
ton, a  close  and  conscientious  observer,  he  told  me  that  he  had  per- 
sonally examined   numerous  quartz-veins,  occurring  all   along  the 
flanks  of  the  Sierra  Nevada,  and  had  found  in  every  case  that  the 
veins,  as  exposed  in  the  deep  canons  cross-cutting  them,  hundreds  of 
feet  below  their  outcrops  on  the  mountains,  were  poorer  in  gold  than, 
at  the  higher  level.     This  testimony  is  valuable,  and  it  may  be  that 
it  indicates  a  general  law  as  to  such    gold-veins ;    but  it  must  be 
borne  in  mind   that  some  of  the  California  gold-mines  have  been 


THE   GENESIS   OF   ORE-DEPOSITS.  245 

worked  deeper  than  any  cafions  have  cut  the  veins.  Yet,  on  the 
other  hand,  many  of  the  deep  gold-mines  of  the  State  have  been 
ultimately  abandoned. 

26.  Mr.  Rickard's  suggestion  has  a  practical  side  of  great  import- 
ance.    Namely,  although,  in  my  judgment,  there  is  no  established 
general  law,  discouraging  the  exploration  of  a  vein  in  depth,  so  long 
as  the  fissfl re  continues  well-defined,  and  especially  if  it  carries  any 
thread  of  ore,  it  is  undoubtedly  the  case  that  mining  explorations  are 
too  much  confined  to  sinking  and  drifting,  and  that  there  is  too  little 
cross-cutting  for  parallel  fissures  and  ore- bodies.     To  some  extent 
this  is  one  of  the  results  of  our  absurd  United  States  mining  law, 
which  lays  so  much  stress  upon  the  "apex  "  and  the  "lode;"  but 
the  mistaken  practice  of  neglecting  cross-cuts  into  the  country-rock 
is  not  confined  to  mines  operated  under  that  law. 

27.  Another  important  point  in  Prof.  Posepny's  paper  is  his  pro- 
position (based  on  Noggerath's  observations  in  the  main,  but  not 
lacking  other  support)  that  open  spaces  of  dissolution  may  be  formed 
by  ascending  as  well  as  descending  currents.     Since  the  process  of 
solution  depends  upon  the  character  of  the  liquid  agent,  this  is  only 
saying  that  some  ascending  waters  may  be  able  to  dissolve  portions 
of  the  rocks  they  traverse ;  and  that  if  such  rocks  belong  to  the  class 
represented  by  limestone,  such  currents  may  produce  in  them  caves 
and  channels,  comparable  to  those  notoriously  produced  by  the  de- 
scending waters.     I  confess,  this  seems  to  me  a  reasonable  proposi- 
tion, however  meager  may  be  the  proofs  thus  far  adduced.     And  I 
cannot  understand,  at  all  events,  how  opponents  of  the  ascension- 
theory  should  object  to  it ;  for  they  do  not  deny  that  there  are  such 
things  as  ascending  mineral  springs,  and  that  these  springs  hold  in 
solution  such  substances  as  carbonates  and  free  carbonic  acid.     What 
they  deny  is  that  these  springs  deposit  anything  in  their  channels. 
In  that  case,  they  must  dissolve  without  redepositing ;  and  the  evi- 
dence that  they  have  actually  excavated  channels  underground  is 
afforded  by  their  constitution.     They  bring  the  evidence  of  their 
guilt  with  them.     To  reply  that  they  are  part  of  the  vadose  circula- 
tion only,  and  hence,  no  matter  what  their  local  direction,  belong  to 
the  descending  branch,  is  not  permissible ;  for  springs  encountered 
at  great  depths  in  mining  have  the  composition  required  to  make 
them  active  solvents.     How  can  it  be  doubted  that  the  hot  waters 
of  the  springs  encountered  in  the  Bohemian  mines  (see  Nos.  1,  2  and 
3  of  Prof.  Posepny's  table,  p.  38),  which  contain  "a  notable  quan- 


246  THE   GENESIS   OF   ORE-DEPOSITS. 

tity  of  free  carbonic  acid,"  would,  if  they  traversed  limestone,  ex- 
cavate cavernous  channels  in  it  ? 

28.  Moreover,  there  is  reason  why  a  liquid  solvent  under  pressure, 
occupying  a  space  in   a  soluble   rock,  should  eat  its  way  upward 
rather  than  downward  or  laterally — namely,  because  the  insoluble 
portions  of  the  rock,  loosened  by  the  action  of  the  solvent,  fall  away 
from   the  roof  of  the  cavity  most  easily  and   completely,  leaving 
fresh  surfaces  open  to,  further  attack.     Whoever  has  visited,  as  I 
have  done,  the  salt-mines  of  the   Salzkammergut,  in  the  Austrian 
Tyrol,  where  salt  is  extracted  by  Sinkwerke,*  and  has  observed  how 
the  great  underground   rooms,  repeatedly  tilled  with  water  under 
pressure,  travel  upward  through  the  mass  of  the  saliferous  rock,  as 
their  roofs  are  attacked  and  dissolved,  while  their  floors  are  rela- 
tively protected  by  the  fallen   insoluble  dibris,  can  scarcely  doubt 
the  possibility  of  the  formation  of  spaces  of  dissolution  by  ascend- 
ing waters.     One  variety  of  this  extraction — viz.,  the  so-called  "con- 
tinuous watering,"  employed  in  some  of  the  mines — presents  a  still 
closer  analogy.     In  that  method  the  water  is  not  introduced  period- 
ically into  each  Sinkwerk,  to  be   withdrawn   when   saturated,  and 
wholly  replaced  with  fresh  water  for  further  solution.     On  the  con- 
trary, the  flow  of  water  is  made  continuous,  fresh  water  being  ad- 
mitted at  one  point  while  saturated   brine  is  conducted  away  at 
another.     It   is   true  that  the  actual  flow  of  the  current  is  down- 
ward, the  fresh  water  being  admitted   above  and  the  brine  drawn 
off  below;  but  this  is  not  an  essential  feature  of  the  process  itself. 
The  actual  progress  of  excavation  by  solution  is  upward,  and  the 
essential  condition  is  the  presence  of  a  pressure  sufficient  to  cause 
the  solvent  to  penetrate  the  roof.     That  being  secured,  the  roof  is 
mainly  attacked,  the  side  much  less,  and  the  bottom  scarcely  at  all. 

29.  Prof.  Posepny's  "  Theory  of  the  Sinking  of  Heavier  Con- 
stituents," as  applied  to  the  distribution  of  gold,  etc.,  in  placers,  is 
a  valuable  addition  to  our  knowledge  of  such  deposits.     It  is  highly 
desirable  that  our  members  engaged  in  placer  or  hydraulic  mining 
should  give  us  the  results  of  careful  observation  upon  the  conditions 
presented  by  the  gold-deposits  of  this  country,     Few  of  them  have 
done  so  thus  far,  and  the  field  is  full  of  interesting  data  not  yet  put 
into  shape  for  preservation.     I  am  inclined  to  think,  for  instance, 
that  "  the  hypothesis  of  a  natural  concentration  in  running  water," 
which  Prof.  Posepny  disparages,  and  for  which  he  proposes  to  sub- 

*  Described  in  Serlo's  Leitfaden  zur  Bergbaukunde,  4th  ed.,  Berlin,  1884,  vol.  i., 
p.  611  et  seq. 


THE   GENESIS   OF   ORE-DEPOSITS.  247 

stitute  the  theory  just  mentioned,  would  find  some  support  in  the 
phenomena  of  many  American  placers,  where  the  gold  is  concen- 
trated not  only  on  a  false  or  true  bed-rock,  but  in  distinct  channels 
along  that  plane,  so  that  the  placer-miners,  for  many  years,  have 
pursued  the  tortuous  channels  of  "  pay-dirt,"  leaving  large  areas  un- 
worked,  which,  for  some  reason  or  other,  did  not  pay,  though  they 
were  equally  "  in  the  gulch,"  and  had  the  bed-rock  under  them,  like 
the  rest.  I  do  not  mean  to  deny  the  possible  agency  of  such  a  con- 
centration by  gravity  in  loose  sands  and  gravels  as  Prof.  Posepny 
has  postulated,  but  I  fancy  it  would  be  hard  to  explain  the  distribu- 
tion of  the  gold  in  many  of  our  American  placers  except  by  includ- 
ing among  its  factors  the  action  of  running  water.  If  I  am  correct 
in  this  impression,  I  may  venture  to  consider  the  case  as  one  in 
which  Prof.  Posepny's  heaviest  artillery  can  be  turned  back  upon 
him;  since  his  theory  of  "settling"  may  be  called  a  sort  of  dry 
"  seepage  "  or  secretion  by  gravity,  and  my  view  may  be  considered 
as  the  assertion  that,  here  as  elsewhere,  there  is  no  deposition  with- 
out circulation. 

Concerning  the  differences  of  opinion  developed  by  this  discus- 
sion, I  think  it  may  be  said  that,  upon  closer  examination,  they  are 
not  important,  except  as  to  the  explanations  of  certain  districts  and 
ore-deposits  which  Prof.  Posepny  has  rather  deduced  from  the  writ- 
ings of  others  than  based  upon  observations  of  his  own. 

With  regard  to  nearly  or  quite  all  of  these  instances,  our  own  ex- 
perts are  not  agreed,  so  that  Prof.  Posepny  has  respectable  backing 
for  his  views,  whether  they  turn  out  in  the  end  to  be  correct  or  not. 
Certainly  he  has  presented  them  with  a  conspicuous  absence  of  dog- 
matism, and  they  have  been  received  on  the  part  of  our  members,  I 
am  happ}7  to  say,  with  the  respect  due  to  the  merits  of  a  veteran  au- 
thority, and  with  gratitude  for  the  generosity  which  has  enriched 
the  Transactions  of  the  Institute  with  one  of  the  most  important 
contributions  to  technical  science  ever  made  through  that  medium. 

F.  M.  F.  CAZIN,  Hoboken,  N.  J.  :  Bergrath  Posepny  rejects  my 
assumption  of  the  presence  of  copper  in  the  Triassic  sea,  claiming 
that  the  evidence  adduced  does  not  hold  good,  and  observing  in  sup- 
port of  his  view,  "  that  these  palms,"  the  cuprified  fossils  of  -which 
are  found  in  the  "  coarse  yellow  sandstones  and  conglomerates  over- 
lying the  red  beds  of  the  Trias,"  "  on  the  junction  of  the  Trias  with 
the  Cretaceous,"*  "  probably  occur  in  a  fresh- water  basin." 

The  fossil  in  question  is  identical  with  "  Podozamites  crassifolia," 

*  J.  S.  Newberry,  Report  on  the  Expedition  of  1859,  pages  117  and  118. 


248  THE    GENESIS   OF   ORE-DEPOSITS. 

described*  as  occurring  in  the  State  of  Sonora.  t  Palms  cover  at 
this  date  a  narrow  belt  along  the  northern  coast  of  South  America, 
disappearing  in  the  interior.  The  location  of  the  Nacimiento  copper- 
belt  is  one,  from  which  the  Cretaceous  sea  retired  last  of  all  on  this 
continent.  Its  waters  at  this  date  are  shed  into  the  Gulf  of  Mexico, 
with  no  indication  anywhere  of  a  pre-existing  barrier.  I  am  ac- 
quainted with  the  English  and  North  German  AVealden  formation, 
having  mined  in  it;  but,  as  J.  S.  NWberry  did  not,  so  I  did  not,  find 
a  trace  of  evidence  for  assuming  a  sweet-water  formation  at  the 
Nacimiento  copper-deposits. 

My  assumption,  therefore,  stands  on  proper  ground,  unless  more 
than  a  probability  to  the  contrary  be  offered. 

If  ever  J.  S.  Newberry's  and  my  own  observations  as  to  the  geo- 
logical position  and  normal  character  of  the  deposits  in  question  have 
been  objected  to  on  the  ground  of  actual  local  observations,  I  am 
ignorant  of  the  fact. 

JOSEPH  LE  CONTE,  Berkeley,  Cal. :  All  geologists,  but  especially 
students  of  the  phenomena  of  metalliferous  veins,  are  under  deep 
obligation  to  Bergrath  Posepuy  for  the  very  lucid  exposition  and 
abundant  illustrations  of  these  phenomena  contained  ui  his  admi- 
rable treatise  on  the  "Genesis  of  Ore-Deposits."  Like  the  previous 
treatise  of  Sandberger,  though  taking  an  extreme  opposite  position, 
it  must  powerfully  revive  the  interest  of  students  and  observers  in 
the  purely  scientific  theory  of  metalliferous  veins.  Although  read 
at  the  International  Engineering  Congress  of  the  World's  Fair  at 
Chicago,  in  1893,  it  has  only  very  recently  fallen  under  my  eye- 
As  I  have  thought  much,  and  published  somewhat  on  this  subject, 
I  beg  leave  to  say  a  few  words  in  the  way  of  criticism  on  this  mas- 
terly work. 

*  Ibid.,  p.  145. 

f  It  is  one  of  the  various  strange  things  observed  in  geological  reports,  that  are 
the  compound  work  of  many — that,  although  J.  S.  Newberry  prominently  and  re- 
peatedly refers  to  the  palm-fossils  of  Nacimiento,  his  plates  show  naught  under  that 
head,  but  do  show  a  true  image  of  these  "  palm-leaves,"  described  as  collected  in 
"quite  a  number"  by  Mr.  Redmond  from  "the  Triassic  strata  at  Los  Broncos, 
Sonora,"  a  locality  not  visited  by  the  expedition  of  which  the  report  is  made.  I 
may  mention  as  an  amusing  coincidence,  that  at  Prof.  Newberry's  and  at  my  time 
there  was  at  Nacimiento  a  silver-smith,  who  hailed  from  Los  Broncos,  Sonora,  and 
who,  whenever  in  his  trade  he  needed  copper,  smelted  it  in  a  miniature  crucible  on 
a  miniature  Mexican  forge  with  accordion-shaped  bellows,  using  as  his  material  for 
copper  the  fossil  palm-leaves  of  Nacimiento,  of  which  within  easy  walk  from  his 
door  he  could  pick  up  all  he  was  in  need  of,  and  of  which  he  kept  on  hand  "quite 
a  number." 


THE   GENESIS   OF   ORE-DEPOSITS.  249 

All,  I  think,  will  agree  that  one  of  the  chief  merits  of  the  work 
consists  in  the  clear  distinction  which  the  author  draws  between  what 
he  calls  the  vadose,  or  superficial,  and  the  deep  circulation  of  under- 
ground water;  the  water  in  the  one  case  containing  air,  and  there- 
fore oxidizing  ;  in  the  other,  destitute  of  air,  and  therefore,  non- 
oxidizing;  the  one  circulation  driven  by  gravity  alone,  the  direc- 
tion of  the  current  being  determined  by  the  place  of  outflow,  the 
other  driven  largely  by  heat  received  in  the  lower  parts  of  its  circuit, 
and  the  direction  of  its  current  being  mainly  upwards. 

We  are  all,  I  think,  especially  pleased  with  the  significance  he 
finds  in,  and  the  importance  he  attaches  to,  the  oxidizing  and  non- 
oxidizing  effects  of  these  two  circulations  respectively.  It  follows, 
from  this  view,  that  metallic  sulphides  are  not  deposited  from  the 
waters  of  the  vadose  circulation,  unless  under  the  exceptional  con- 
ditions of  the  presence  of  excess  of  organic  matter;  and  therefore, 
that  the  presence  of  metals  in  the  form  of  sulphides  is  usually  a 
sign  of  deposit  from  ascending  currents  of  the  deeper  non-oxidizing 
circulation. 

Most  of  us,  I  think,  too  (and  I  among  the  number),  will  agree 
with  him,  as  against  Sandberger,  that  since  great  deep  fissures  are 
not  empty,  air-filled  spaces,  but  are  necessarily  filled  with  water, 
deposits  in  them  cannot  take  place  by  seepage  or  oozing,  or  lateral 
secretion  from  the  immediate  bounding- walls.  Also,  that  the  phe- 
nomena of  crustification  or  ribbon-structure  of  vein-contents  seem 
to  negative  such  a  mode  of  filling  as  is  supposed  by  Sandberger; 
that  this  structure  does  not  indicate  a  filling  by  oozing  and  trickling 
of  waters  containing  soluble  matters,  down  on  a  free  surface,  but 
rather  a  deposit  in  successive  layers  inward  from  water  contained  in 
the  fissure. 

For  all  this,  and  very  much  more  which  I  cannot  repeat  here,  we 
are  under  many  obligations  to  Bergrath  Posepny.  Nevertheless,  I 
cannot  but  think  that  he  carries  his  ascension -views  much  too  far; 
that  in  his  zeal  against  the  extreme  lateral -secret  ion  views  of  Sand- 
berger, he  has  gone  to  the  other  extreme  of  ascensionism ;  and  that 
a  truer  view  than  either  may  be  found  in  one  that  shall  combine 
and  reconcile  these  two  extremes. 

The  evidence  of  the  extremeness  of  his  views  is  found,  and  in- 
deed, is  embodied,  in  his  use  of  the  term  barysphere.  As  contrasted 
with  lithosphere,  this  term  can  only  mean  a  region  in  the  interior  of 
the  earth,  the  materials  of  which  are  heavier,  because  more  metal- 
liferous, than  the  superficial  lithosphere  visible  to  us.  From  such 


250  THE   GENESIS   OF   ORE-DEPOSITS. 

a  metalliferous  barysphere,  he  thinks,  all  the  inetals  of  ore-deposits 
(with  trifling  exceptions)  are  derived.  It  is  true,  that  in  his  reply 
to  objectors,  he  speaks  of  his  barysphere  as  only  the  equivalent  of  the 
"  unknown  depths  "  of  other  writers ;  but,  it  must  be  remarked,  that 
this  latter  term,  while  open  to  the  objection  of  indefiniteness,  does 
not,  necessarily,  carry  with  it  any  implication  of  a  region  peculiar 
in  its  density  and  in  the  abundance  of  its  metallic  contents,  although 
it  is  doubtless  often  used  with  this  implication.  The  word  bary- 
sphere, on  the  other  hand,  fixes  definitely  an  idea  which  has  long 
floated  vaguely  in  the  minds  of  many  writers  on  this  subject.  It 
will,  therefore,  form  the  central  point  of  my  criticism. 

I. — Is  THERE  A  BARYSPHERE  WITHIN  REACH  OF  CIRCU- 
LATING WATER  ? 

It  is  true,  that  the  earth  increases  in  density  from  the  surface  to- 
wards the  center,  and  probably  to  the  very  center  itself.  This  is 
shown  by  the  fact  that  the  mean  density  of  the  earth  is  more  than 
double  that  of  the  superficial  parts.  It  is  true,  also,  that  the  increas- 
ing density,  while  certainly  due,  in  part,  to  condensation  by  increas- 
ing pressure,  is  probably  also  due,  in  part,  to  difference  of  material, 
and  especially  to  the  presence  of  metals,  as  sulphides  or  native,  in 
greater  abundance  in  the  interior  parts.  It  is  true,  therefore,  that 
the  deeper  parts  of  the  earth  are  certainly  heavier,  and  probably  more 
metalliferous,  than  the  superficial  parts.  In  a  word,  it  is  true  that 
there  is  a  barysphere,  and  probably  in  the  sense  used  by  Posepny, 
as  being  more  metalliferous.  But  how  deep  must  we  go  to  find  this 
barysphere?  Let  us  see. 

Taking  the  density  of  the  superficial  parts  of  the  earth  (or  what 
Posepny  would  call  the  lithosphere)  at  2.5,  and  the  mean  density  of 
the  earth  as  a  whole  at  5.5  (Posepny  accepts  these  figures),  and  as- 
suming the  simplest  rate  of  increase,  viz.,  a  uniform  rate,  then  an 
actual  density  equal  to  the  mean  density  of  5.5  would  be  reached  at 
the  depth  of  1000  miles,  and  the  central  density  would  be  14.5* 
This  is  an  increase  of  3  in  1000  miles.  At  the  depth  of  100  miles, 
therefore,  the  increase  would  be  0.3  and  the  density  only  2.8.  Is 
it  at  all  probable  that  we  ever  have  circulating  water  coming  up  from 
any  such  depth  as  100  miles  ?  And  yet,  2.8  is  only  about  the  den- 

*  By  mathematical  calculation  based  on  the  above  conditions,  an  actual  density 
equal  to  the  mean  density  of  5.5  is  reached  at  depth  of  £  radius  from  the  surface. 
Multiplying  this  gain  of  3  by  4  and  adding  the  surface  density  of  2.5  makes  a  cen- 
tral density  of  14.5  (3  X  4  -f  2.5  =  14.5.) 


THE   GENESIS   OP   ORE-DEPOSITS.  251 

sity  of  our  more  basic  eruptives,  and  therefore,  wholly  undeserving 
the  name  of  a  barysphere.  Circulating  water  may  possibly  come  up 
from  as  deep  as  10  miles,  but,  at  the  same  rate  of  increase,  the  den- 
sity there  is  only  2.53 — an  increase  over  the  superficial  density 
wholly  inappreciable.  Dr.  Raymond,  interpreting  Posepny,  defines 
the  barysphere  as  all  that  interior  region,  the  circulating  water  of 
which  would  not  come  up  at  all  without  the  aid  of  heat.  Does  this 
mean  all  but  the  superficial  region  traversed  by  the  vadose  or  oxi- 
dizing circulation  ?  If  so,  it  cannot  be  far  from  the  surface,  and 
the  term  barysphere,  as  applied  to  it,  is  surely  wholly  inappropriate 
and  misleading. 

But  it  may  be  answered  that  all  this  reasoning  is  based  on  the 
assumption  of  a  uniform  rate  of  increase  of  interior  density;  while 
in  fact  the  great  mean  density  of  the  earth  may  be  explained  by  the 
existence  of  a  highly  metalliferous  shell  at  no  great  distance  be- 
neath the  surface  and  therefore  within  easy  reach  of  circulating 
waters.  To  this  view  I  make  the  following  objections  : 

1.  All  our  general  reasonings  concerning  the  cause  of  the  great 
mean  density  of  the  earth,  whether  (a)  condensation  by   increasing 
pressure,  or  (b)  arrangement  of  materials  of  a  primal  fused  earth  ac- 
cording to  their  relative  specific  gravities,  would   make  the  increase 
progressive  to  the  center.    In  fact  it  is  hard  to  conceive  the  conditions 
under  which  a  dense  metalliferous  shell  a  little  way  beneath  the  sur- 
face could  be  formed.* 

2.  We  have  abundance  of  materials  coming  up  in  eruptions  from 
depths  as  great  as  circulating  water  is  ever  likely  to  reach,  and  yet 
these  materials  show  no  such  density  and  metalliferousness  as  is  im- 
plied in  the  term  barysphere. 

But  again,  it  may  be  objected  that  I  greatly  underestimate  the 
depth  which  may  be  reached  by  underground  water.  This  brings 
up  an  important  but  difficult  question.  Is  there  any  limit  to  the 
depth  to  which  meteoric  water  may  penetrate  ?  If  so,  what  deter- 
mines the  limit  and  where  is  it?  These  are  questions  which  science 
is  probably  not  yet  prepared  to  answer  definitely.  I  once  thought, 


*  Of  the  two  causes  mentioned  above,  the  first  would  probably  produce  increase  at 
an  increasing  rate  and  put  the  place  of  density  equal  to  mean  density  deeper  than  | 
radius  down.  The  second  might  give  rise  to  any  kind  of  rate  according  to  the  rela- 
tive amount  of  the  different  kinds  of  metals;  but  not  improbably  to  a  decreasing 
rate  and  put  the  place  of  mean  density  higher.  The  combination  of  these  two 
would  make  an  indeterminable  rate ;  but  something  like  a  uniform  rate  is  as  proba- 
ble as,  perhaps  more  probable,  than  any  other. 


252  THE   GENESIS   OF   ORE-DEPOSITS. 

that  since  the  pressure  of  a  water-column  increases  uniformly  with 
the  depth,  while  the  elastic  tension  of  steam  in  contact  with  water 
increases  with  increasing  heat  at  an  increasing  rate,  so  as  to  develop 
a  logarithmic  curve,  there  must  be  a  depth  at  which  the  tension  of 
steam  would  be  equal  to  the  downward  pressure  and  that  at  that 
depth  would  be  found  the  limit  of  underground  water ;  and  I  ex- 
pressed this  conclusion  in  my  Elements  of  Geology,  page  99.  Fur- 
ther reflection  has  convinced  me  that  the  conclusion  is  unwarranted. 
Such  a  limit  would  undoubtedly  be  reached  if  the  increase  of  ten- 
sion continued  to  follow  the  same  law  indefinitely.  But  it  is  now 
known  that  at  a  certain  temperature,  called  the  critical  point,  steam 
has  the  same  density  as  the  water  from  which  it  is  formed.  At  this 
point,  therefore,  it  may  be  regarded  as  either  steam  or  water  indif- 
ferently, and  under  the  slightest  change  of  temperature  it  takes  the 
one  form  or  the  other.  Beyond  this  point  it  is  no  longer  steam  in 
contact  with  water,  but  dry  steam,  which  we  know  follows  an  en- 
tirely different  law.  Now  the  critical  point  of  water  is  about  700° 
F.  and  the  tension  of  steam  at  this  point  is  about  200  atmospheres. 
Taking  the  increase  of  underground  temperature  at  1°  for  53  feet, 
or  100°  per  mile,  the  temperature  of  700°  would  be  found  at  the 
depth  of  seven  miles.  But  the  pressure  of  a  water-column  there 
would  be  about  1100  atmospheres.  The  tension  has  not  yet  even 
nearly  reached  the  pressure ;  and,  as  the  law  changes  here,  it  would 
seem  that  the  tension  would  never  overtake  the  hydrostatic  pressure 
at  all.  Therefore,  if  the  underground  water  is  limited  at  all  in  its 
downward  course,  as  is  probably  the  case,  it  must  be  limited  in  some 
other  way,  probably  by  increasing  compactness  of  material,  under 
the  increasing  pressure  of  superincumbent  rock,  which,  by  closing  up 
the  pores  would  inhibit  further  penetration,  or  would  make  it  easier 
for  the  water  to  come  up  again  in  ascending  currents. 

I  think  we  may  reasonably  conclude,  therefore,  that  whether  there 
be  a  limit  to  underground  water  or  not,  it  is  certain  that  below  a 
certain  moderate  depth,  say  8  or  10  miles,  such  water  cannot  be 
circulating ;  for  beyond  this  the  compactness  of  rock  under  super- 
incumbent pressure  would  be  such,  that  while  capillarity  and  weight 
of  water-column  might  still  urge  further  movement,  passages  suf- 
ficiently open  to  allow  currents  of  circulation  could  not  exist. 

We  may  assume,  then,  that  the  limit  of  circulating  water  cannot, 
be  more  than  10  miles  in  depth.     Below  this,  water  may  indeed 
penetrate  by  capillarity  and  by  weight  of  its  own  column,  but  such 
water  does  not  enter  into  ordinary  circulation,  although  it  may  come 


THE    GENESIS   OF   QBE-DEPOSITS.  253 

up  in  volcanic  eruptions  and  indeed  supply  the  force  of  such  erup- 
tions. Still,  below  this  again,  and  even  to  the  very  center,  there 
may  possibly  be  what  Fisher  calls  constituent  water,  i.e.,  original 
water  occluded  in  the  primal  fused  magma  of  the  earth,  still  pres- 
ent in  the  interior  and  coming  up  in  volcanoes  and  (according  to 
him),  the  cause  of  their  eruptions.  If  there  be  such,  it  is  not  cir- 
culating water  in  the  ordinary  sense,  and  therefore  may  be  left  out 
of  account  in  this  discussion. 

Underground  water  may  be  conceived,  therefore,  as  existing  in 
three  possible  conditions,  but  more  and  more  doubtfully  in  the  order 
named  : 

1.  Circulating   meteoric  water.      This    of  course   is  certain.     It 
probably  extends  but  a  few  miles  (8  or  10)  below  the  surface. 

2.  Meteoric  water,  but  not  circulating.     The  existence  of  this  is 
probable.  I  have  been  accustomed  to  call  it  u  volcanic"  water,  because 
it  is  a  probable  source  of  the  eruptive  force  of  volcanoes. 

3.  Constituent  water,  originally  occluded  in  the  primal  magma  of 
the  incandescent  fused  earth,  and  still  occluded  in  the  materials  of 
the  interior.     This,  Fisher  thinks,  is  still  escaping,  and  in  doing  so, 
fuses  its  way  towards  the^  surface,  and  finally  emerges  in  volcanic 
eruptions.     This,  of  course,  is  very  doubtful. 

Of  these  three,  if  they  all  exist,  we  are  concerned,  I  believe,  with 
the  first  only. 

We  have  assumed  10  miles  as  the  limit  of  circulating  water,  and 
therefore  the  limit  of  depth  from  which  metals  may  be  derived. 
But  at  that  depth,  as  already  shown,  there  is  no  "barysphere"  in 
any  intelligible  sense  of  that  word.  For  the  difference  in  density 
and  in  metalliferous  ness  between  the  rocks  there  and  those  at  the 
surface  is  quite  inappreciable.  We  have,  in  fact,  much  material 
coming  up  from  this  very  region,  and  therefore  know  its  density. 
Our  more  basic  rocks  are  indeed  far  denser  and  more  metalliferous 
than  the  average  of  that  region,  having  acquired  greater  density  by 
differentiation  from  an  average  magma  representing  that  region. 

I  believe,  therefore,  that  the  greater  abundance  of  metallic  ores  in 
solution  in  ascending  waters  is  the  result,  not  of  the  greater  abund- 
ance of  metals  in  their  lower  courses,  but  of  the  greater  heat  which 
they  take  up  in  that  part  of  their  course  and  the  greater  pressure  to 
which  they  have  been  subjected  there.  Both  heat  and  pressure 
greatly  increase  the  solvent  power  of  water  upon  the  feebly  soluble 
metallic  sulphides.  Thus  heavily  freighted,  the  waters  lose,  in 
ascending,  both  heat  and  pressure,  and  therefore  deposit  abundantly 


254  THE   GENESIS   OF   ORE-DEPOSITS. 

in  their  upward  course.  In  a  word,  ascending  waters  are  rich  in 
metallic  contents,  not  because  they  have  traversed  a  barysphere,  but 
because  they  have  traversed  a  thermosphere.  With  equal  heat  and 
pressure,  I  am  convinced,  they  would  get  as  much  metal  from  our 
more  basic  rocks  here  at  the  surface  as  they  now  do  from  the  hypo- 
thetical barysphere.  These  ascending  waters  are  non-oxidizing,  not 
because  they  have  never  seen  the  air,  i.e.,  are  not  meteoric,  but  be- 
cause they  have  exhausted  their  oxidizing  power  by  previous  oxida- 
tion of  metals,  of  organic  matters,  and  other  oxidable  substances  in 
the  upper  parts  of  their  downward  course. 

II. — VADOSE  vs.  DEEP  CIRCULATION. 

Again,  I  think,  Posepny  draws  much  too  sharp  a  distinction  be- 
tween his  two  kinds  of  circulation ;  not  indeed  as  to  their  oxidizing 
and  non-oxidizing  properties,  but  as  to  the  force  of  circulation  in 
the  two  cases  respectively.  In  his  anxiety  to  distinguish  them 
sharply,  he  speaks  as  if  the  forces  of  circulation  in  the  two  cases 
were  entirely  different,  being  gravity  or  hydrostatic  pressure  in  the 
once  case  and  heat  and  capillarity  in  the  other.  Now  nothing  can 
be  more  certain  than  that  hydrostatic  pressure  is  the  fundamental 
cause  in  both  cases  alike;  although  heat,  by  lightening  the  ascend- 
ing column  and  thus  disturbing  the  hydrostatic  equilibrium,  is  the 
immediately  determining  cause  in  the.  latter.  As  Mr.  Rickard,  in  the 
discussion,  has  justly  pointed  out,  the  effect  of  heat  in  the  under- 
ground circulation  is  exactly  like  its  effect  in  determining  circulation 
in  a  system  of  house-warming  pipes. 

Again,  Posepny  lays  much  stress  on  capillarity  as  an  additional 
force  urging  forward  the  circulation.  But  surely  this  cannot  be  so. 
Capillarity  is  indeed  a  powerful  force,  urging  water  to  where  there 
is  none,  but  an  equally  powerful  force  fixing  it  where  it  is.  So  far 
from  assisting,  it  powerfully  impedes  circulation,  and,  where  it  is 
strong  enough,  inhibits  it  altogether.  Dry  clay  is  a  powerful  ab- 
sorber of  water,  but,  when  once  wet,  it  becomes  impermeable  to  cir- 
culation. 

In  fact,  Posepny  sometimes  speaks  of  the  deep  barysphere  circu- 
lation, as  contrasted  with  the  vadose  circulation,  in  such  terms  that 
one  is  left  in  serious  doubt  whether  he  regards  the  former  as  meteoric 
water  at  all ;  and  yet  he  speaks  of  it  as  circulating.  Sometimes  it 
seems  as  if  he  regarded  his  vadose  water  alone  as  meteoric  and  hi.s 
barysphere  water  as  some  other  kind  of  water  coming  up  from  the 
deep  interior  of  the  earth,  like,  for  example,  the  constituent  water 


THE   GENESIS   OF   ORE-DEPOSITS.  255 

of  Fisher.  Such  water,  if  there  be  any  such,  might  indeed  be  con- 
ceived as  coming  up  from  a  metalliferous  barysphere,  such  as  he 
supposes.  But  this  would  be  escaping  water,  not  circulating  water. 
If  he  means  anything  like  this,  it  ought  to  be  distinctly  stated,  for 
it  changes  entirely  the  ground  of  the  discussion,  and  much  that  I 
have  said  above  would  be  wide  of  the  mark.  For  my  own  part, 
unless  we  adopt  Fisher's  view,  I  believe  that  we  never  have  any 
water  coming  up  which  has  not  previously  gone  down.  This  is 
what  is  meant  by  circulation,  but  1  cannot  think  Posepny  can  mean 
that  his  deep  circulating  water  is  not  meteoric;  and  I  therefore  say 
nothing  more  on  this  head. 

III. — LEACHING  OF  WALL-ROCK. 

Again,  although  I  fully  agree  with  Posepny  and  his  brilliant  ex- 
positor, Dr.  Raymond,  that  crustification,  when  it  is  well  developed, 
indicates  deposit  from  within,  by  ascending  waters  already  occupy- 
ing the  fissure,  and  not  by  laterally  incoming  water  depositing  in 
the  act  of  incoming  (in  the  manner  of  seepage-water  in  empty  cavi- 
ties), yet  I  cannot  agree  with  them  in  thinking  that  the  pressure  of 
such  ascending  water  would  necessarily  or  even  usually  prevent  the 
incoming  of  lateral  currents  from  the  wall-rock.  It  is  doubtless 
true  that  the  ascending  water  in  the  fissure  is  under  higher  pressure 
than  precisely  similar  water  on  the  outside;  for,  in  addition  to  the 
hydrostatic  pressure  determined  by  the  height  of  the  outlet,  it  is 
also  under  hydraulic  pressure  in  proportion  to  the  velocity  of  the 
upward  current.  But  the  water  saturating  the  wall-rock  is  also,  of 
course,  under  heavy  hydrostatic  pressure.  And  when  we  remember 
the  slowness  of  the  ascending  current  (which  is  a  necessary  condition 
for  deposit),  and  therefore  the  slight  excess  of  the  pressure  over  that 
measured  by  the  height  of  its  outlet ;  and  when  we  remember  fur- 
ther that  the  ascending  water  is  hot  while  the  wall- water  is  cooler, 
and  therefore  denser,  we  may  well  doubt  whether  the  pressure  of 
the  ascending  or  the  lateral  waters  will  be  the  greater,  and  therefore 
whether  the  current  will  set  outward  or  inward.  The  pressure  of 
the  ascending  water  is  greater  by  virtue  of  its  motion,  but  that  of 
the  wall-rock  is  greater  by  virtue  of  its  greater  density.  It  seems 
not  unreasonable,  therefore,  to  conclude  that  sometimes  and  in  some 
places  the  current  would  set  outward,  and  sometimes  and  in  some 
places  it  would  set  inward.  In  many  places,  doubtless,  the  wall-rock  is 
not  saturated.  In  such  places,  of  course,  the  current  would  set  out- 
ward by  capillarity,  as  well  as  by  pressure,  until  saturation  is  reached. 


256  THE   GENESIS   OF   ORE-DEPOSITS. 

Of  course,  also,  impediments  to  upward  flow,  brought  about  by  fill- 
ing of  the  fissure  by  deposit  or  otherwise,  would  increase  the  inte- 
rior pressure,  and  would  cause  an  upward  ramification  and  outflow 
in  many  places  at  the  surface. 

Although  the  analogy  is  by  no  means  perfect,  yet,  by  way  of  illus- 
tration, the  ascending  fissure-current,  with  its  freight  of  dissolved 
matters  and  its  tributary  drainage  from  the  country-walls,  may  be 
roughly  compared  to  a  main  river  with  its  freight  of  suspended 
materials  and  its  lateral  tributaries.  In  such  a  stream,  the  tributa- 
ries usually  discharge  freely  into  the  main  river,  increasing  its  vol- 
ume, though  perhaps  diminishing  its  percentage  of  freight;  but 
sometimes,  by  the  greater  pressure  of  flood- waters,  the  main  stream 
may  back  up  the  tributaries  until  equilibrium  is  restored.  So  in 
the  case  before  us,  the  main  ascending  fissure-stream,  with  its  freight 
of  dissolved  matters,  usually  receives  tributaries  from  the  wall-rock, 
although,  by  defect  of  pressure  of  the  latter  or  increased  pressure  of 
the  former,  the  main  current  may  overflow  into  the  wall-rock. 
Again,  in  both  cases,  the  percentage  of  freight  is  usually  greatest  in 
the  main  stream,  and  therefore  the  deposits  by  diminished  velocity 
and  carrying  power  in  the  one  case  and  by  diminished  heat  and 
pressure  and  solvent  power  in  the  other,  are  heaviest  there,  although, 
sometimes,  heavy  deposits  occur  also  in  the  back  waters.  Again,  in 
both  cases,  while  the  tributaries  increase  the  volume  of  the  current, 
they  usually  diminish  the  percentage  of  freight,  although  sometimes 
the  reverse  may  be  the  fact.  Finally,  as  rivers,  when  obstructed  by 
their  own  deposits,  may  reach  their  final  destination  by  inverse  rami- 
fication and  through  many  mouths ;  so  ascending  fissure-currents, 
obstructed  by  their  own  deposits,  may  branch  upward  and  reach  the 
surface  by  many  exits.  This,  however,  can  be  seen  only  in  ascend- 
ing currents  still  depositing,  as  in  the  cases  of  Sulphur  Bank  and 
Steamboat  Springs.  In  most  cases  this  part  of  their  course  has  been 
carried  away  by  erosion. 

In  a  word,  there  seems  no  reasonable  doubt  that  while  usually  the 
main  deposits  have  been  brought  up  from  below,  yet  the  tributaries 
from  the  country-wall  do  contribute,  and  sometimes  in  an  impor- 
tant degree,  to  the  metallic  contents  of  the  veins.  This  seems  well- 
nigh  proved  in  those  cases  given  by  Sandberger  and  Becker,  in  which 
analyses,  especially  selective  analyses,  find  notable  quantities  of  tha 
required  metals  in  the  more  basic  minerals  of  the  country  wall-rock. 
To  discredit  the  obvious  inferences  from  the  results  of  a  method  so 
much  in  accord  with  modern  science  and  substitute  a  roundabout 


THE   GENESIS   OF   ORE-DEPOSITS.  257 

I 

process  of  secondary  leachings  by  vadose  circulation  of  primary  im- 
pregnations derived  from  a  hypothetical  barysphere,  as  Posepny 
does,  must  be  regarded  as  a  return  to  the  speculative  methods  of 
early  writers.  Again,  in  cases  like  the  lead-ores  of  Missouri  and 
Wisconsin,  where  there  is  no  evidence  of  disturbance  or  of  igneous 
agency  of  any  kind,  is  it  not  more  rational  to  derive  the  metals  from 
the  wall-rock,  though  probably  from  its  deeper  parts,  than  from  an 
unknown  barysphere? 

IV. — A  MORE  COMPREHENSIVE  THEORY  NEEDED. 

In  conclusion,  I  cannot  but  think  that  the  views  brought  forward 
in  1883  in  my  paper  on  the  "Genesis  of  Metalliferous  Veins"  (Am. 
Jour,  of  Sci.,  vol.  xxvi.,  p.  1,  1883),  although  I  would  perhaps  now 
modify  them  slightly  on  some  points,  still  represent  well  the  present 
condition  of  science  on  this  subject.  Those  who  ha.ve  read  that 
paper  will  remember  that  it  is  an  attempt  based  partly  on  my  own 
investigations  of  the  phenomena  of  metalliferous  vein-formation  now 
going  on  at  Sulphur  Bank  and  at  Steamboat  Springs,  and  partly  on 
a  general  survey  of  the  whole  field,  to  embody  a  comprehensive  and 
rational  theory,  avoiding  extremes  on  both  hands.  In  it  I  devoted 
considerable  space  to  combating  the  extreme  lateral-secretion  views  of 
Sandberger.  I  did  so  because,  on  account  of  the  recent  appearance 
and  signal  ability  of  his  treatise,  it  seemed  likely  to  do  harm  by 
carrying  scientific  opinion  too  far  in  one  direction.  If  it  had  been 
Posepny's  treatise  instead  of  Sandberger's,  I  should  have  felt  equally 
compelled  to  combat  it,  and  on  the  same  ground.  Posepny  quotes 
freely  from  my  papers  on  "Sulphur  Bank  "  and  on  "Steamboat 
Springs,"  but  not  from  that  on  "Genesis  of  Metalliferous  Veins." 
Whether  he  has  seen  it,  I  do  not  know. 

There  has  always  been,  and  still  is,  a  strong  tendency  to  extreme 
views  on  this  subject.  On  the  one  hand,  ascensionists  would  derive 
all  metals  from  a  mysterious  metalliferous  region — a  "  barysphere," 
and  so  strong  is  their  advocacy  that  even  when  analysis  finds  the 
required  metals  in  notable  quantities  in  the  wall-rock,  they  discredit* 
the  obvious  inference  by  suggesting  a  secondary  leaching  of  mate- 
rials deposited  there  by  primary  baryspheric  currents.  On  the  other 
hand,  the  lateral-secretionists  would  derive  metals  not  from  ascend- 
ing currents  at  all,  but  wholly  from  direct  secretion  from  the  imme- 
diate bounding- walls;  and  so  strong  is  their  advocacy  that  even 
when  the  deposit  of  metals  from  hot  ascending  currents  is  proved 
by  direct  observation,  as  at  Sulphur  Bank  and  at  Steamboat  Springs, 

17 


258  THE   GENESIS   OF   ORE-DEPOSITS. 

I 

they  seek  to  throw  discredit  on  the  obvious  inference  in  regard  to 
all  metalliferous  veins,  by  giving  many  cases  in  which  hot  springs 
do  not  deposit  any  metals.  My  paper  was  an  earnest  attempt  to 
combine  what  is  true  in  each,  and  thus  to  reconcile  these  extremes 
by  a  more  comprehensive  view,  which  explains  their  differences. 

According  to  my  view,  the  source  of  metais  is,  indeed,  on  the  one 
hand,  by  leaching,  but  not  by  lateral  secretion  ;  on  the  other  hand, 
not  from  a  hypothetical  barysphere,  but  from  the  wall-rock  ;  though, 
again,  not  from  all  parts  alike,  but  mainly  from  the  deepest  parts, 
and  even  from  below  the  deepest  parts,  of  sensible  fissures.  As  in 
the  case  of  many  other  disputes,  I  believe  both  sides  are  right  and 
both  are  wrong.  Ascensionists  are  right  in  deriving  metals  mainly 
by  ascending  currents  from  great  depths,  but  wrong  in  imagining 
these  depths  to  be  an  exceptionally  metalliferous  barysphere.  They 
are  wrong  also  in  not  allowing  subordinate  contributions  by  lateral 
currents  from  the  wall-rock  higher  up.  The  lateral-secretionists,  on 
the  other  hand,  are  right  in  deriving  metals  by  leaching  from  the  wall- 
rock,  but  wrong  in  not  making  the  main  source  the  thermosphere. 

In  the  uncolored  light  of  a  more  comprehensive  view,  many  of 
the  difficulties  and  obscurities  of  the  subject  disappear. 

1.  Ore-deposits,  using  the  term  in  its  widest  sense,  may  take  place 
from  many  kinds  of  waters,  but  especially  from  alkaline  solutions; 
for  these  are  the  natural  solvents  of  metallic  sulphides,  and  metallic 
sulphides  are  usually  the  original  form  of  such  deposits. 

2.  They  may  take   place   from    waters  at  any  temperature  and 
pressure,  but   mainly  from   those  at  high   temperature  and  under 
heavy  pressure,  because,  on   account  of  their  great  solvent  power, 
such  waters  are  heavily  freighted  with  metals. 

3.  The  depositing  waters  may  be  moving  in  any  direction — up- 
coming, horizontally  moving  or  even   sometimes  down-going,  but 
mainly  up-coming,  because  by  losing  heat  and  pressure  at  every 
step,  such  waters  are  sure  to  deposit  abundantly. 

4.  Deposits  may  take  place  in  any  kind  of  water-ways — in  open 
fissures,  in  incipient  fissures,  joints,  cracks  and  even  in  porous  sand- 
stone, but  especially  in  great  open   fissures,  because  these  are  the 
main  highways  of  ascending  waters  from  the  greatest  depths. 

5.  Deposits  may  be  found  in  many  regions  and  in  many  kinds  of 
rocks,  but  mainly  in    mountain-regions  and  in  metamorphic   andi 
igneous  rocks,  because  the  thermosphere  is  nearer  the  surface,  and 
ready  access  thereto  through  great  fissures  is  found  mostly  in  these 
regions  and  in  these  rocks. 


INDEX. 


[NOTE. — In  this  Index  the  names  of  Contributors  to  the  Discussion  are  printed  in 
small  capitals.] 

ERRATUM. 

For  correction  of  Fahrenheit  degrees  on  page  37,  see  page  174. 


Alford,  C.  A.,  on  geology  of  the  Transvaal,  149. 

Alte  Hoffnung  Erbstollen  silver-mine,  Mitweida,  Saxony,  character  of  ground-water 
at.  26. 

O 

Ammeberg,  Sweden,  character  of  zinc-blende  deposits  at,  130. 

Analyses  of;  filling  of  fissure  veins,  34  ;  gas  liberated  from  warm  mineral  water,  32  ; 
mineral  waters,  38 ;  waters  encountered  in  mines,  38. 

Andreasberg,  Hartz  mountains,  silver-ore  veins  of,  74. 

'Arizona:  copper-deposits,  100,  120;  Hillside  mine,  mineral  veins  of,  197. 

Arsenic  in  mineral  waters,  43. 

Ascending  waters :  carbonic  acid  the  most  important  geological  factor,  41 ;  en- 
countered in  mines,  26  ;  heat  of,  28  et  seq.  ;  hydrogen  sulphide  in,  40. 

Australasia,  gold-deposits  of,  148,  204  et  seq. 

"  Banded  structure  "  and  "  crustifiration,"  189, 222,  239. 

Barysphere:  the  source  at  unknown  depths  of  ore-deposits,  10,  67,  74,  185,  223,  243, 
249;  does  it  exist  within  reach  of  circulating  waters  ?  250. 

Beaumont,  Elie  de,  theory  of  "  pentagonal  symmetry"  of,  7. 

BECKER,  G.  F. :  in  discussion  of  the  genesis  of  ore-deposits,  189;  analysis  of  filling 
of  fissure  veins,  34  ;  on  underground  temperature,  28. 

Belcher  silver  mine,  Storey  county,  Nev.,  location  of  bonanza,  84. 

Bell,  E.,  on  ore-deposits  of  Sudbury,  Can.,  134. 

Bescheert  Gliick  silver-mine,  Freiberg,  Saxony,  character  of  deposit,  72. 

Bischof,  G. :  arsenic  in  mineral  waters  found  by,  43;  on  metallic  deposits  from  sea- 
water,  111. 

BLAKE,  W.  P. :  in  discussion  of  the  genesis  of  ore-deposits,  174;  on  ore-deposits  in 
Copper  Basin,  Arizona,  121. 

Bobierre,  A.,  amount  of  salt  in  rain-water  found  by,  40. 

Bohemia:  ancient  gold-workings  in  Trauteuau  region,  149;  copper-sandstones  of,  116; 
Jcupferschiefer  of,  113 ;  ore-deposits  at  Przibram,  52,  56,  70,  76,  220  et  seq. ;  tem- 
perature of  thermal  springs,  37;  tin-placers  at  Flatten,  146. 

Bohneisenerz  deposits,  125. 

Botesiti  gold-field,  Dacian  district,  Transylvania,  81. 

Calamine-deposits  at  Raibl,  Carinthia,  122, 

Caledonia  gold-mine,  Thames  district,  New  Zealand,  richness  of  ore,  205. 
California,  character  of  copper-ores  in  peninsula  of  Lower,  121. 
California  silver-mine,  Storey  county,  Nev.,  location  of  bonanza,  84. 
Canada,  ore-deposits  of  Sudbury,  133,  194. 

Carbonic  acid  an  important  geological  factor  in  ascending  waters,  41. 

* 


260  INDEX. 

Carinthia:  analogy  of  Bleiberg  ore-deposits  with  those  of  Eureka  district,  Nev.,  102; 
calamine-deposits  of  Kaibl,  122 ;  ore-deposits  at  Raibl,  56,  64,  93. 

Carlsbad  Sprudel :  analysis  and  temperature  of  water,  37,  38 ;  character  of  deposit.  49. 

Carniola,  Bohneisenerz  at  Wochein,  125. 

Cavities  in  rocks,  character  of  filling,  13. 

CAZIN,  F.  M.  F. :  in  discussion  of  the  genesis  of  ore-deposits,  191,  247;  on  copper-ores 
of  New  Mexico,  120. 

Chemical  constitution  of  mineral  waters,  36. 

CHURCH,  JOHN  A. :  in  discussion  of  the  genesis  of  ore-deposits,  180  ;  on  Justice  silver- 
mine,  221 ;  on  source  of  underground  waters,  28. 

Churpriuz  silver-mine,  Freiberg,  Saxony,  ascending  mineral  waters  at,  26. 

Cinnabar-deposits  of  Sulphur  Bank,  Cal.,  29  et  seq.,  61. 

Classification  of  ore-deposits:  systems  employed  hitherto,  3;  proposed  modification 
of,  195,  209. 

Clausthal,  Hartz  mountains,  ore-deposits,  72. 

Cohen,  E.,  on  Witwatersrand  gold-deposits,  South  Africa,  148. 

Colorado:  Red  Mountain  district,  Ouray  county,  character  of  ore-deposits,  100;  ore- 
deposits  of  Leadville,  97. 

Comstock  Lode,  Storey  county,  Nev. :  geological  conditions  of,  82 ;  heat  of  ascending 
waters  at,  28 ;  ore-deposition  of,  180,  221. 

Conical  mounds  built  by  ascending  mineral  waters,  35. 

Consolidated  Virginia  silver-mine,  Storey  county.  Nev.,  location  of  bonanza,  84. 

Copper-ores:  Arizona,  100,  120;  Bohemia,  113,  116;  Lake  Superior  district,  132; 
Lower  California,  121;  Mannsfeld,  113;  New  Mexico,  100,  120,  194;  Prettau,  Ty- 
rol, 131;  St.  Avoid,  116;  Sweden,  129;  Vermont,  191;  Westphalia,  114. 

Copper-sandstone  of  Bohemia,  116. 

Cornwall,  England,  tin-deposits  of,  127. 

Cotta:  classification  of  ore-deposits  by,  4;  on  ore-deposition,  113  et  seq. 

"  Gratification  :"  11,  183,  189,  222,  239,  255. 

Crystalline  schists,  ore-deposits  in,  125. 

Cumberland,  England,  iron-ore  deposits,  125. 

Dacian  gold-fields,  Transylvania,  79,  89. 

Dakota,  gold-deposits  of  Black  Hills,  147. 

Daubree,  Prof.  A.:  on  alterations  produced  by  mineral  springs,  44  et  seq.;  on  causes 

of  striae  on  lode-walls,  197 ;  on  subterranean  water-circulation,  16  et  seq.   - 
Deep  underground  circulation,  24. 
De  Lauuay,  chemical  theory  of  ore-deposits  of,  7,  58. 
Detrital  deposits,  140. 

Devereux,  W.  B.,  on  occurrence  of  gold  in  Black  Hills,  Dak.,  147. 
Discission,  spaces  of,  12,  68. 
Dissolution,  spaces  of,  12,  87. 
Dux  coal-mine  (lignite),  Bohemia,  irruption  of  thermal  waters  at,  27. 

East  Wheal  Lovell  tin-mine,  Cornwall,  Eng.,  character  of  ore-body,  128. 

Einigkeit  silver-mine,  Joachirnsthal,  Saxony,  ascending  mineral  springs  at,  27. 

Emmens,  S.  H.,  on  decomposition  of  metals,  137. 

EMMONS,  S.  F.,  in  discussion  of  the  genesis  of  ore-deposits,  184 ;  on  descending  waters, 
98. 

England:   iron-ores  of  Cumberland,  125;  lead-mining  in  north  of,  96. 

Erbsenstein,  deposits  of,  at  Carlsbad,  49. 

Eruptive  rocks:  deposits  in,  125;  influence  on  ore-deposition,  177;  relation  of  ther- 
mal springs  to,  204. 

Erzgebirge,  mineral  springs  in  mines  of,  27;  ore-deposits,  75. 

Eureka  district,  Nev.,  geological  conditions  of,  103. 


INDEX.  261 

Fissures:  of  dislocation,  13;  filling,  analysis  of,  34  ;  ore-deposits  in,  68;  theories  of 

origin  of,  196. 

Foster,  C.  Le  Neve,  on  tin-deposits  of  Cornwall,  127. 
Foullon,  A.  B.  von,  on  ore-deposits  of  Sudbnry,  Can.,  133,  134. 
France,  Fontainebleau  sandstone,  109. 
Freiberg,  Germany,  ore-deposits,  72. 

Freihung,  Bavarian  Upper  Palatinate,  lead-deposits,  118. 
Fuchs,  E.,  on  copper-ores  of  lower  California,  121. 

Gage,  J.  F.,  on  occurrence  of  lead-  and  zinc-ores  in  Missouri.  106. 

Galena,  tree-stems  changed  to,  at  Vesuvius  lead-mines,  Bavaria,  118. 

Gas,  analysis  of,  liberated  from  warm  mineral  water,  32. 

Geodes,  opal  and  chalcedony,  mineral  deposits  in,  22. 

Germany:  copper-ores,  113  etseq,,  iron-oi'e  deposits  of  Alsace,  125;  lead-deposits  of 
Mechernich,  near  Commern,  117;  tin-placers  at  Annaberg,  Saxony,  146. 

Gold  :  ancient  placer-mining  in  Bohemia,  149;  occurrence  of,  in  manganese  spar,  62. 

Gold  Hill  silver  mine,  Storey  county,  Nev.,  high  temperature  of  water  in,  28. 

Gold-ores  :  of  Australasia,  148,  204  et  seq.;  Beresov,  Ural  mountains,  70;  deposits  of  Black 
Hills,  Dak.,  147:  Hungary,  78:  New  Zealand:  Hauraki  or  Thames  gold-field, 
204;  Otago  gold-field,  207;  South  Africa,  Witwatersrand,  148;  Sweden,  Falun, 
129;  Transylvania,  Dacian  gold-field,  79;  in  the  Ural  mountains,  70,  141;  Ver- 
espatak,  Transylvania,  60,  80. 

Gottes  Geschick  silver-mine,  Schwarzenberg,  Saxony,  ascending  waters  at,  26. 

Great  Extended  Hustlers  gold-mine,  Victoria,  Australia,  character  of  quartz  at,  199. 

Greece,  ore-deposits  of  Laurium,  123,  227. 

Grimm,  J. :  classification  of  ore-deposits  by,  4;  examination  of  Transylvania  ore- 
deposits  by,  88. 

Groddeck,  A.  von :  on  ore-deposition,  112  et  seq. ;  system  of  classification  of  ore-de- 
posits, 4. 

Ground-water,  movements  of,  17. 

Hale  and  Norcross  silver-mine,  Comstock  Lode,  Nev.,  flooding  of,  by  water,  28. 
Hartz  mountains^  ore  deposits  of,  72. 
Hauraki  or  Thames  gold-field,  New  Zealand,  204. 
Helmhacker,  E.,  on  ore-deposits  of  Altai  region,  Siberia,  142. 
Hillside  gold-  and  silver-mine,  Arizona,  mineral  veins  of,  197. 
Hoefer,  H.,  on  metallic  deposits  from  sea-water,  111. 
Hot  mineral  waters  encountered  in  mines,  28. 

Hungary :  geode  of  iron  opal  from  Dreiwasser,  22  ;  ore-deposits  of,  78  et  seq. ;  silver- 
deposits  of  Eezbanya,  90. 

Hydrogen  sulphide,  important  part  of,  in  ascending  waters,  40. 
Hysterogenites,  15. 
Hysteromorphous  ore-deposits,  135. 

Idiogenous  mineral  deposits,  9. 

Iron  opal,  geode  of,  from  Dreiwasser,  Hungary,  22. 

Iron-ores:  analogy  of  Bohemian,  and  Michigan,  219;  deposition  of,  in  Mesabi  range. 
Minn.,  211;  England,  Cumberland,  125;  Germany,  Alsace,  125;  Lake  Superior 
deposits,  210;  Norway,  127  et  seq.;  Spain,  Eio  Tinto  (limonite),  136;  Sweden, 
Taberg  (magnetite),  126 ;  Switzerland,  Carniola,  125 ;  Tyrol,  131. 

Joachimsthal  mines,  Bohemia,  mineral  waters  of,  27. 

Justice  silver-mine,  Storey  county,  Nev.,  character  of  ore-deposit,  84,  184,  221. 

Kakar  district,  southern  Ural,  Eussia,  ore-deposits  of,  143. 


262  INDEX. 

Katrontza  gold-mine,  Verespatak,  Transylvania,  character  of  ore  at,  60,  62. 
Kendall,  J.  D.,  on  iron-ores  of  Cumberland,  Eng.,  125. 
Kerr,  W.  C.,  on  North  Carolina  gold-deposits,  140, 
Kjerulf,  Th.,  on  iron-ore  deposits  in  Norway,  127. 
Kupferschiefer  of  Mannsfeld,  Thuringia  and  Bohemia,  113. 

Lake  Superior  region:  copper-deposits,  132;  iron-ores  of,  210. 

Lapparent,  A.  de,  on  metamorphism,  108. 

Lateral -secret!  011  theory  of  ore-deposition,  52  et  seq.,  176,  185,  219,  224,  235,  238,  249. 

Laurium,  Greece,  ore-deposits,  123,  227. 

Leaching  of  wall-rock,  255. 

LE  CONTE,  PROF.  JOSEPH  :  in  discussion  of  the  genesis  of  ore-deposits,  248  ;  on  min- 
eral vein-formation,  30  et  seq. 

Lead-ores:  Freihuug,  Bavarian  upper  Palatinate,  118;  Mechernich,  near  Conimern, 
Germany,  117 ;  Missouri  and  Wisconsin,  105 ;  North  of  England,  96. 

Leadville,  Colo.,  ore-deposits,  97. 

Limestone:  copper-deposits  in,  100;  lead-deposits* in  carboniferous,  in  England,  96; 
mineral  deposits  in  caves,  22;  ore-bearing,  in  Carinthia,  93. 

Lock,  A.  G.,  on  gold-deposits,  140. 

Lottner,  classification  of  ore-deposits  by,  6. 

Manner  of  filling  open  spaces  in  general,  58. 

Mannsfeld  Jcupferschiefer,  113. 

Marine  detritis,  143. 

Mdtyas  Kiraly  gold-mine,  Verespatak,  Transylvania,  character  of  native  gold  at,  62,  65. 

Mesabi  range,  Minn.,  iron-ores  of,  211. 

Metals  found  in  mineral  waters,  42. 

Metamorphous  ore-deposits,  108  el  seq. 

Metasomasis,  first  use  of  term,  5,  180. 

Metasomatic  ore-deposits  in  soluble  rocks,  122,  231. 

Mine  La  Motte,  Madison  county,  Mo.,  lead-deposits  at,  107. 

Mineral  deposits :  in  geodes,  22 :  hysterornorphous,  135 ;  idiogenous  and  xeuogenous, 

9  et  seq.'  in  limestone  caves,  22  ;  metamorphous,  108. 
Mineral  springs :  structural  features  of  deposits  of,  48  ;  at  the  surface,  34. 
Mineral  waters:  alterations  produced  by,  44;  analyses  of,  33,  38  ei  seq. ;  arsenic  in,  43; 

chemical  constitution  of,  36;  minute  metallic  admixtures  in,  42  ;  temperature  of, 

37  (see  Erratum,  174). 

Missouri :  lead  regions  of,  105 ;  ore-deposits  of,  174  et  seq. 
Moanataeri  gold-mine,  Thames  district,  New  Zealand,  richness  of  ore,  205. 
Miiller,  H.,  on  mineral  springs,  26. 

Nevada :  character  of  ore-deposits,  101 ;  Comstock  Lode,  28,  82,  180,  221 ;  Steamboat 

Springs,  thermal  waters  of,  33  et  seq. 

Newberry,  Prof.  J.  S. :  on  classification  of  ore-deposits,  7;  on  origin  of  ores,  120. 
New  Mexico,  copper-deposits,  100,  120, 194. 

New  Zealand :  gold  in  Coal-Measures  of,  148 ;  gold-fields  of,  204  et  seq. 
Noggerath,  J.,  on  alterations  produced  by  mineral  waters,  45,  92,  186,  226. 
North  Iron  Hill,  Lake  county,  Colo.,  ore-deposits  of,  187  et  seq. 
North  Ophir  silver-mine,  Comstock  Lode,  Nev.,  high  temperature  of  water  in,  28. 
Norway,  iron-ore  deposits,  127,  128. 

Offenbdnya  gold-mines,  Dacian  district,  Transylvania,  79,  89. 

Ore-deposition:  of  Comstock  Lode,  Storey  county,  Nev.,  180;  in  fresh  water,  112;  in- 
fluence of  eruptive  rocks,  177;  John  Woodward's  opinions,  two  hundred  years 


INDEX.  263 

ago,  178;  lateral-secretion  theory,  52  et  seq.,  176,  185,  219,  224,  235,  238,  249;  in 
open  spaces,  58,  180,  220;  from  sea-water,  110. 

Ore-deposits :  chemical  views  of  French  school,  7, 58  ;  classification  hitherto  employed, 
3  ;  in  crystalline  schists  and  eruptive  rocks,  125;  detrital,  141 ;  example  of  classes 
of,  66;  formed  by  chemical  and  mechanical  influences  of  surface  region,  135; 
hysteromorphous,  135;  hysterornorphous,  of  older  geological  formation,  146; 
metamorphous,  108;  metasomatic,  in  soluble  rocks,  122;  origin  of,  in  deep  regions, 
51 ;  proposed  classification  of,  195,  209 ;  in  soluble  rocks,  87 ;  verchovilcy,  or  sur- 
face, 139. 

Ore-veins:  in  the  neighborhood  of  eruptive  masses,  75;  in  stratified  rocks,  73:  wholly 
within  large  eruptive  formations,  78. 

Origin  of  ore-deposits  in  the  deep  regions,  51. 

Otago  gold-field,  New  Zealand,  geological  formation  of,  207. 

Phillips,  J.  A.:  classification  of  ore-deposits  by,  7;  on  appearance  of  gold  at  Besseges, 

France,  149. 

Placer  ore-deposits,  144. 
Platinum,  placer-deposits  of,  144. 

Poutgibaud  silver-lead  district,  France,  formation  of  lodes,  205. 
POSEPNY,  PROF.,  in  discussion  of  his  paper,  215. 
Prettau  in  Tyrol,  copper-mines  of,  131. 
Przibram,  Bohemia,  ore-deposits,  52,  56,  70,  76,  220  et  seq. 
Przibram  Mining  Academy,  study  of  geology  at,  8, 
Pseudomorphs,  phenomena  in  formation  of,  14. 
Pumpelly,  R, :  classification  of  ore-deposits  by,  6;  on  Lake  Superior  copper-deposits, 

132. 


Queensland,  gold  in  Coal-Measures  of,  148. 
Quick-silver  at  Sulphur  Bank,  Gal.,  29  et  seq. 


Raibl,  Carinthia,  ore-deposits,  56,  64,  93,  122. 

Rain-water,  salt  in,  40. 

RAYMOND,  R.  W. :  in  discussion  of  the  genesis  of  ore-deposits,  209,  232;  on  classifica- 
tion of  ore-deposits,  6,  209. 

Red  Mountain  district,  Colo.,  character  of  ore-deposits,  100. 

Reichenstein  silver-mine,  Valle  Sacca,  Hungary,  description  of  ore-deposit,  91. 

Reyer,  Dr.  E..  on  tin  placer-deposits,  145. 

Rezbanya,  Hungary,  geology  of  ore-deposits  at,  90. 

RICKARD,  T.  A. :  in  discussion  of  the  genesis  of  ore-deposits,  176,  195. 

Rio  Tinto,  Spain,  limonite-deposits  at,  136. 

Rock-cavities,  mineral  deposits  in,  13. 

Rock-salt  deposits;  of  the  Persian  Gulf,  19  ;  at  Maros  Ujvar,  Transylvania,  19. 

Rodna,  Transylvania,  ore-deposits,  87. 

Russia:  gold-placer-deposits  of  Ural  Mountains,  141;  ore-deposits  of  Kackar  district, 
in  the  Ural,  143. 

Salt,  in  rain-water,  40. 

Salt-mining  in  Austrian  Tyrol,  246. 

Sandberger,  Dr. :  lateral -secretion,  theory  of,  52  et  seq.,  176, 185, 219,  224,  235,  238,  249; 

Przibrani  rock,  analysis  of  samples  by,  57. 

Sandstones :  copper,  of  Bohemia,  116 ;  at  Fontainebleau,  France,  109. 
Savage  silver-mine,  Comstock  Lode,  Nev.,  flood  of  water  in,  28. 
Sawyer,  A.  R.,  on  Witwatersrand  gold-field,  South  Africa,  149. 
Scandinavia,  ore-deposits  of,  128. 
Schists:  copper,  113  et  seq.;  ore-deposits  in  crystalline,  125. 


264  INDEX. 

Sea-water:  metallic  sulphides  from,  174;  traces  of  metals  in,  110. 

Seven-Thirty  silver-mine,  Clear  Creek  county,  Colo.,  ore-veins  of,  200. 

Siberia,  Altai  region,  ore  deposits  of,  142. 

Silver-  and  silver-lead-ores :  in  Colorado,  189,  200;  Hartz  mountains,  74 ;  at  Lauriuni, 

Greece,  123;  Nevada,  102,  184,  229;  Pontgibaud,  France,  205;  at  Raibl,  Cariuthia, 

93;  at  Rezbanya,  Hungary,  90. 
Silver  Reef  mining  district,  Utah,  119. 
Sjogreu,  A.,  on  iron-ore  deposits  in  Sweden,  127. 
Slickensides  :  formation  of,  197  et  seq. ;  at  Raibl  silver-lead-miues,  94  ;  in  Scandinavian 

mines,  128. 

Spaces  of  discission,  12;  ore-deposits  in,  68. 
Spaces  of  dissolution,  12. 
Spain,  iron-ore  deposits  of,  126. 
South  Africa,  gold-deposits  of,  148. 
St.  Avoid,  copper-ores  in  sandstone  of.  116. 

Steamboat  Springs,  Washoe  county,  Nev.,  thermal  waters  of,  33  tt  seq. 
Stelzner,  Dr.  A.  W. :  on  deposits  of  tin-ore,  146;  term  of  "  metasomasis "  proposed, 

by,  5. 

Stream  detritus,  141. 

Strise  and  slickensides  as  proofs  of  movement.  197  et  seq. 
Structural  features  of  the  deposits  of  mineral  springs,  48. 
Struggl  silver-lead-miue,  Raibl,  Carinthia,  ore-bodies  of,  95. 
Subterranean  water-circulation,  16,  202,  234. 
Subterranean  waters,  heat  of  ascending,  28. 
Sulphur  Bank  quicksilver-mine,  Lake  county,  Cal.,  thermal  waters  at,  29  et  seq.; 

236. 

o 

Sweden:  Ammeberg,  zinc-bleude-miue  at,  130;  copper-  and  gold-ores,  129:  Taberg, 

iron-ore  deposits  of,  126. 
Switzerland,  Camiola,  iron-ore  deposits,  125. 

Taberg,  Sweden,  iron-ore  deposits,  126. 

Talhawang  gold-district,  New  South  Wales,  148. 

Tasmania,  gold  in  Coal-Measures  of,  148. 

Temperature  of  mineral  waters,  37  (see  Erratum,  174). 

Thames  gold-field,  New  Zealand,  204. 

Thermal  waters  encountered  in  mines,  27. 

Thuringia,  Icupferschiefer  of,  113. 

Tin-deposits:  of  Cornwall,  England,  127;  formation  of,  127;  placer-deposits,  145. 

Transvaal,  South  Africa,  Witwatersraud  gold-fields,  148. 

Transylvania:  Dacian  gold-district,  79:  mining  rock-salt  at  Maros  Ujva"r,  19;  Veres- 

patak  gold  deposits,  60  et  seq.,  80  ;  Vulkoj  gold  deposits,  80. 
Tyrol:  copper-mines  of  Prettau,  131;  iron-ore  deposits,  131;  salt-mining  at  the  Salz- 

kammergut,  246. 

Ural  mountains,  gold -districts  of,  70. 

Utah :  character  of  ore-deposits,  101,  119 ;  Silver  Reef  mining  district,  119. 

Vadose  vs.  deep  circulation,  254. 

Vadose  underground  circulation,  17;  filling  of  open  spaces  formed  by,  21;  probable 

source  of  some  deep  ore-deposits,  183. 

Valle"  lead-mines,  Jefferson  county,  Mo.,  character  of  deposits,  65, 106. 
Verchwiky,  or  surface  ore-deposits,  139. 

Verespatak,  Transylvania,  structure  of  gold-deposits  at,  60,  80. 
Vermont,  copper-deposits  of,  191. 

Vesuvius  lead-mine,  Bavaria,  Germany,  tree-stems  changed  to  galena  at,  118. 
Vulkoj  gold-mines,  Transylvania,  character  of  ore-deposits  of,  80. 


INDEX.  265 

Waldenstein,  classification  of  ore-deposits  by,  4. 

Waters:  analysis  of,  from  mineral  springs,  33,  38 ;  ascending,  encountered  in  mines, 

26 :  subterranean  circulation  of,  16,  202,  234. 
Werner,  A.,  theory  of  ore-deposits  of,  3. 

Westphalia,  copper-ores  of,  114  ;  pisolitic  formation  at  Warstein,  62. 
Whitney,  Prof.  J.  D. :  classification  of  mineral  deposits  by,  6;  on  lead-  and  zinc-ores 

of  Wisconsin,  108. 

WINCHELL,  HOKACE  V. :  in  discussion  of  the  genesis  of  ore-deposits,  178,  210. 
Winklehner,  H.,  on  rock-salt  deposits  of  the  Persian  Gulf,  19. 
WINSLOW,  ARTHUR:  in  discussion  of  the  genesis  of  ore-deposits,  174. 
Wisconsin,  lead-  and  zinc-regions  of,  105, 107,  175  et  seq. 
Witwatersrand  gold-field,  Transvaal,  South  Africa,  148. 
Woodward,  John,  "  Essay  Towards  a  Natural  History  of  the  Earth,"  by,  178. 

Xenogenites  in  general,  11. 
Xeuogenous  mineral  deposits,  9. 

Yellow  Jacket  silver-mine,  Storey  county,  Nev.,  location  of  ore,  84. 
Yellowstone  National  Park ;  analysis  of  waters,  38 ;  chimney -like  conduits  built  by 
geysers,  35. 

o 

Zinc-ores:  Ammeberg,  Sweden,  130;  Wisconsin,  107,  175  et  seq. 
Zoppe,  G.,  on  salt  in  rain-water,  40. 


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